SEO terms, explained for developers
No marketing fluff. Clear definitions, code examples, and practical context for every SEO concept you need to know.
Robots.txt
Robots.txt is a plain text file at the root of a website that instructs search engine crawlers which URLs they are allowed or disallowed from accessing.
Sitemap XML
An XML sitemap is a file that lists URLs on your website along with optional metadata (last modified date, change frequency, priority) to help search engines discover and crawl your pages.
Core Web Vitals
Core Web Vitals are a set of three Google metrics — Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS) — that measure real-world user experience.
Crawl Budget
Crawl budget is the number of URLs Googlebot will crawl on your site within a given period, determined by crawl rate limit (server capacity) and crawl demand (page importance).
301 Redirect
A 301 redirect is an HTTP status code that permanently redirects one URL to another, telling search engines to transfer ranking signals (link equity) to the new URL.
404 Error
A 404 error is an HTTP status code indicating that the server cannot find the requested URL. It signals to search engines that the page does not exist.
Hreflang
Hreflang is an HTML attribute that specifies the language and optional geographic targeting of a page, helping search engines serve the correct version to users in different regions.
Page Speed
Page speed is the measurement of how quickly a web page's content loads and becomes interactive, typically measured by metrics like Time to First Byte (TTFB), First Contentful Paint (FCP), and Largest Contentful Paint (LCP).
Mobile-First Indexing
Mobile-first indexing means Google predominantly uses the mobile version of a website's content for indexing and ranking, rather than the desktop version.
XML Sitemap
An XML sitemap is a structured XML file that lists the URLs on your website, providing search engines with a roadmap for discovering and prioritizing content for crawling.
Technical SEO
Technical SEO encompasses the server-side and infrastructure optimizations that help search engines efficiently crawl, render, index, and rank your website's content.
Largest Contentful Paint (LCP)
Largest Contentful Paint (LCP) is a Core Web Vital metric that measures the time from when the page starts loading to when the largest text block or image element is rendered in the viewport.
Interaction to Next Paint (INP)
Interaction to Next Paint (INP) is a Core Web Vital metric that measures the latency of all user interactions (clicks, taps, key presses) throughout the page lifecycle, reporting the worst interaction minus outliers.
Cumulative Layout Shift (CLS)
Cumulative Layout Shift (CLS) is a Core Web Vital metric that quantifies how much visible content unexpectedly shifts during the page lifecycle, measuring visual stability.
Time to First Byte (TTFB)
Time to First Byte (TTFB) is a metric that measures the duration between a user's HTTP request and the first byte of the server's response reaching the browser.
First Contentful Paint (FCP)
First Contentful Paint (FCP) is a performance metric that measures the time from when the page starts loading to when any part of the page's content (text, image, SVG, or canvas element) is rendered on screen.
Crawlability
Crawlability is the ability of search engine crawlers to access, navigate, and read the content of your website's pages without encountering technical barriers.
Renderability
Renderability is the ability of search engine crawlers to execute JavaScript and render a page's content as it would appear to a user in a browser.
JavaScript SEO
JavaScript SEO is the practice of optimizing JavaScript-heavy web applications so that search engines can effectively crawl, render, index, and rank their content.
Server-Side Rendering (SSR)
Server-side rendering (SSR) is a technique where the web server generates the complete HTML for a page on each request, sending fully rendered content to the browser and search engine crawlers.
Static Site Generation (SSG)
Static Site Generation (SSG) is a rendering strategy where pages are pre-rendered as static HTML files at build time, served directly from a CDN without server computation on each request.
Incremental Static Regeneration (ISR)
Incremental Static Regeneration (ISR) is a Next.js rendering strategy that allows statically generated pages to be updated after deployment, either on a timed schedule or on-demand, without a full rebuild.
Dynamic Rendering
Dynamic rendering is a technique that detects search engine crawlers and serves them a pre-rendered HTML version of a page, while serving the regular JavaScript-rendered version to human users.
URL Structure
URL structure refers to the format, hierarchy, and naming conventions of your website's addresses, which communicate page content and site organization to both users and search engines.
Slug
A slug is the human-readable, URL-friendly portion of a web address that identifies a specific page, typically derived from the page title using lowercase letters, numbers, and hyphens.
Permalink
A permalink (permanent link) is a URL that is intended to remain unchanged indefinitely, serving as a stable reference to a specific piece of content.
Sitemap Index
A sitemap index is an XML file that references multiple sitemap files, allowing large websites to organize their URLs across several sitemaps while staying within the 50,000 URL per-sitemap protocol limit.
Pagination SEO
Pagination SEO is the practice of structuring multi-page content series (blog archives, product listings, search results) so that search engines can discover and index all pages efficiently.
Infinite Scroll SEO
Infinite scroll SEO addresses the challenge of making dynamically loaded, scroll-triggered content accessible to search engine crawlers that do not scroll or interact with pages.
Lazy Loading
Lazy loading is a technique that defers the loading of non-critical resources (images, iframes, components) until they are about to enter the viewport, reducing initial page load time.
Image Optimization
Image optimization is the process of reducing image file sizes and serving appropriately sized images to improve page load performance, using techniques like compression, modern formats, and responsive delivery.
WebP
WebP is an image format developed by Google that provides lossy and lossless compression, typically producing files 25-35% smaller than JPEG and PNG at equivalent visual quality.
AVIF
AVIF (AV1 Image File Format) is a modern, royalty-free image format based on the AV1 video codec that delivers significantly better compression than WebP and JPEG while maintaining high visual quality.
Next.js Image Component
The Next.js `<Image>` component (`next/image`) is a built-in extension of the HTML `<img>` tag that provides automatic image optimization including lazy loading, responsive sizing, format conversion, and layout shift prevention.
Font Optimization
Font optimization encompasses techniques to minimize the performance impact of custom web fonts, including self-hosting, subsetting, proper loading strategies, and preventing layout shifts from font swaps.
Code Splitting
Code splitting is a technique that breaks a JavaScript application into smaller chunks (bundles) that are loaded on demand, reducing the initial payload size and improving page load performance.
Tree Shaking
Tree shaking is a dead code elimination technique used by modern JavaScript bundlers that removes unused exports from modules during the build process, producing smaller production bundles.
HTTP Status Codes
HTTP status codes are three-digit numbers returned by a web server in response to a client request, indicating whether the request was successful, redirected, resulted in an error, or failed on the server.
302 Redirect
A 302 redirect is an HTTP status code indicating a temporary redirect — the original URL should be retained in the search index because the redirect is not permanent.
410 Gone
The 410 Gone HTTP status code indicates that a resource has been intentionally and permanently removed, with no forwarding address. It is a stronger signal than 404 for search engine deindexing.
503 Service Unavailable
The 503 Service Unavailable HTTP status code indicates the server is temporarily unable to handle the request, typically due to maintenance or overload, and that the situation is expected to be temporary.
Soft 404
A soft 404 is a web page that displays a "not found" or empty message to users but returns an HTTP 200 (OK) status code instead of the correct 404 status code, misleading search engines about the page's existence.
Orphan Pages
Orphan pages are web pages that exist on a website but have no internal links pointing to them from any other page on the site, making them effectively invisible to crawlers that rely on link discovery.
Site Architecture
Site architecture is the hierarchical structure and organization of a website's pages, URLs, and navigation, determining how content is grouped, linked, and accessed by users and search engine crawlers.
Geo-Targeting
Geo-targeting is the practice of delivering different content, language versions, or regional variations of a website to users based on their geographic location, using technical signals like hreflang, ccTLDs, or server-side detection.
Meta Description
A meta description is an HTML meta tag that provides a brief summary of a web page's content. Search engines often display it as the snippet below the title in search results.
Structured Data
Structured data is a standardized format (typically JSON-LD using schema.org vocabulary) embedded in your HTML that explicitly describes the content of a page to search engines.
Schema Markup
Schema markup is code (usually JSON-LD) that uses the schema.org vocabulary to annotate web content, enabling search engines to display enhanced results like rich snippets.
Open Graph
Open Graph (OG) is a protocol created by Facebook that uses meta tags to control how URLs are displayed when shared on social media platforms.
Breadcrumbs
Breadcrumbs are a navigation pattern that shows the hierarchical path from the homepage to the current page, helping users understand their location within the site structure.
Alt Text
Alt text (alternative text) is an HTML attribute on `<img>` tags that provides a text description of an image for screen readers, search engine crawlers, and situations where the image cannot be displayed.
Title Tag
The title tag is an HTML element (`<title>`) that specifies the title of a web page. It appears in search engine results, browser tabs, and social media shares as the primary clickable headline.
Duplicate Content
Duplicate content refers to identical or substantially similar content appearing at multiple URLs, which can confuse search engines about which version to index and rank.
Thin Content
Thin content refers to web pages that provide little or no unique value to users — pages with minimal text, auto-generated content, or content that is substantially duplicated from other sources.
Keyword Cannibalization
Keyword cannibalization occurs when multiple pages on the same website target the same keyword or search intent, causing them to compete against each other in search results.
On-Page SEO
On-page SEO refers to the optimization of individual web page elements — content, HTML tags, structured data, and internal links — to improve search engine rankings and user experience.
Anchor Text
Anchor text is the visible, clickable text of a hyperlink that provides context to both users and search engines about the content of the linked page.
Search Intent
Search intent (user intent) is the underlying goal a user has when typing a query into a search engine. Google classifies intent into four types: informational, navigational, commercial investigation, and transactional.
Long-Tail Keywords
Long-tail keywords are specific, multi-word search queries that individually have lower search volume but collectively account for the majority of all searches, and typically convert at higher rates.
Keyword Density
Keyword density is the percentage of times a target keyword or phrase appears on a page relative to the total word count. It was once a primary optimization metric but is now largely outdated.
Keyword Research
Keyword research is the process of discovering, analyzing, and selecting search terms that your target audience uses, in order to guide content creation and SEO strategy.
Topical Authority
Topical authority is a site's demonstrated depth of expertise on a specific subject, built by publishing comprehensive, interlinked content that covers a topic from multiple angles.
Content Cluster
A content cluster is a group of thematically related pages organized around a central pillar page, with subtopic pages linking back to the pillar and to each other, creating a semantic web of expertise.
Pillar Page
A pillar page is a comprehensive, long-form piece of content that covers a broad topic at a high level and links to more detailed subtopic pages (cluster content), serving as the central hub of a content cluster.
Hub and Spoke Model
The hub and spoke model is a content architecture pattern where a central hub page (comprehensive overview) links to multiple spoke pages (detailed subtopics), and each spoke links back to the hub.
Silo Structure
Silo structure is a website architecture pattern that groups topically related content into isolated sections (silos), with strong internal linking within each silo and minimal cross-linking between silos.
Entity SEO
Entity SEO is the practice of establishing and optimizing your website's topics, brand, and content as distinct entities within Google's Knowledge Graph, using structured data, consistent signals, and authoritative references.
Semantic SEO
Semantic SEO is an optimization approach that focuses on the meaning, context, and relationships between concepts rather than exact keyword matching, aligning with how modern search engines understand language.
Backlinks
Backlinks (inbound links) are hyperlinks from external websites that point to your site. They act as votes of confidence and are a major ranking factor for search engines.
Internal Linking
Internal linking is the practice of connecting pages within the same website using hyperlinks. It distributes link equity, establishes site hierarchy, and aids crawlability.
Domain Authority
Domain Authority (DA) is a search engine ranking score developed by Moz that predicts how likely a website is to rank in search results, measured on a logarithmic scale from 0 to 100.
Off-Page SEO
Off-page SEO encompasses all optimization activities performed outside of your website to improve its search engine rankings, primarily focused on building backlinks and brand authority.
Link Building
Link building is the practice of acquiring hyperlinks from external websites to your own, with the goal of improving search engine rankings through increased authority and trust signals.
E-E-A-T
E-E-A-T (Experience, Expertise, Authoritativeness, Trustworthiness) is a framework from Google's Search Quality Rater Guidelines used to assess the quality and credibility of web content and its creators.
Link Equity
Link equity (also called link juice or PageRank) is the value and authority that a hyperlink passes from the linking page to the target page, influencing the target's ranking potential.
Domain Rating
Domain Rating (DR) is a proprietary metric by Ahrefs that measures the strength of a website's backlink profile on a logarithmic scale from 0 to 100.
Page Authority
Page Authority (PA) is a Moz metric that predicts how well a specific page will rank in search results, measured on a logarithmic 0-100 scale based on the page's own link profile and other factors.
Local SEO
Local SEO is the practice of optimizing a business's online presence to attract more customers from relevant local searches, primarily through Google Business Profile, local citations, and location-specific content.
Canonical URL
A canonical URL is an HTML link element that tells search engines which URL is the preferred version of a page, consolidating ranking signals when multiple URLs serve similar content.
Indexation
Indexation is the process by which search engines discover, crawl, and store web pages in their database (index) so they can be returned in search results.
Noindex
Noindex is a robots meta tag directive that instructs search engines to exclude a page from their search index, preventing it from appearing in search results.
Nofollow
Nofollow is a link attribute (`rel="nofollow"`) that tells search engines not to pass PageRank (link equity) through a specific link, treating it as a hint rather than a directive.
IndexNow
IndexNow is an open protocol that allows websites to instantly notify search engines about URL changes (new, updated, or deleted pages), enabling faster discovery and indexing.
Google Indexing API
The Google Indexing API is a Google service that allows website owners to directly request crawling and indexing of specific URLs, officially designed for job posting and livestream content.
Robots Meta Tag
The robots meta tag is an HTML element in the `<head>` that provides page-level instructions to search engine crawlers about indexing and link-following behavior.
X-Robots-Tag
X-Robots-Tag is an HTTP response header that provides the same indexing directives as the robots meta tag but can be applied to any file type, including PDFs, images, videos, and API responses.
rel="alternate"
The `rel="alternate"` HTML link attribute identifies an alternative version of the current page, commonly used with hreflang for multilingual sites and with media queries for mobile-specific URLs.
SERP
SERP (Search Engine Results Page) is the page displayed by a search engine in response to a query, containing organic results, paid ads, featured snippets, knowledge panels, and other search features.
Featured Snippet
A featured snippet is a special search result that displays an extracted answer from a web page at the top of Google's organic results (position zero), before the regular listings.
Rich Snippet
A rich snippet is an enhanced search result that displays additional information beyond the standard title, URL, and description — such as star ratings, prices, FAQs, or event dates — powered by structured data.
Bounce Rate
Bounce rate is the percentage of sessions where a user leaves your site after viewing only a single page without any meaningful interaction, as redefined in Google Analytics 4 (GA4).
Click-Through Rate (CTR)
Click-through rate (CTR) is the percentage of users who click on your search result after seeing it in the SERP, calculated as clicks divided by impressions.
Dwell Time
Dwell time is the duration a user spends on a page after clicking a search result and before returning to the search results page, used as an implicit user satisfaction signal.
Pogo-Sticking
Pogo-sticking is a search behavior pattern where a user clicks a search result, quickly returns to the SERP, and clicks a different result — indicating the first page did not satisfy their query.
Google Search Console
Google Search Console (GSC) is a free service by Google that helps website owners monitor, maintain, and troubleshoot their site's presence in Google Search results.
Google Analytics
Google Analytics (GA4) is a free web analytics service by Google that tracks and reports website traffic, user behavior, engagement metrics, and conversion events.
Knowledge Panel
A Knowledge Panel is an information box that appears on the right side of Google search results, displaying verified facts about entities (organizations, people, places, things) drawn from Google's Knowledge Graph.
People Also Ask
People Also Ask (PAA) is a Google SERP feature that displays a list of related questions with expandable answers sourced from web pages, helping users explore topics without new searches.
Zero-Click Search
A zero-click search occurs when a user's query is answered directly on the search engine results page through featured snippets, knowledge panels, calculators, or AI overviews, eliminating the need to click through to any website.
AI Overview (SGE)
AI Overview (formerly Search Generative Experience / SGE) is Google's AI-powered feature that generates a synthesized answer at the top of search results, drawing from multiple web sources to directly respond to user queries.