atlookup

SEO Glossary

Every SEO term, in plain English.

160+ terms across technical SEO, AI Overviews, Core Web Vitals, content quality, and more.

Performance & Core Web Vitals 15 terms

Core Web Vitals

Three real-user metrics — LCP, INP, and CLS — that Google uses as ranking signals.

Largest Contentful Paint (LCP)

How quickly the largest visible element on a page renders. Should be under 2.5s on mobile.

Interaction to Next Paint (INP)

How quickly a page responds to user input. Replaced FID in 2024. Target under 200ms.

Cumulative Layout Shift (CLS)

How much the layout shifts unexpectedly during page load. Target under 0.1.

First Input Delay (FID)

Legacy metric for input responsiveness. Replaced by INP in March 2024.

Time to First Byte (TTFB)

Server response time before the first byte arrives. Target under 600ms.

First Contentful Paint (FCP)

Time until the first DOM content (text, image) appears. Target under 1.8s.

Total Blocking Time (TBT)

Total time main thread was blocked between FCP and TTI. Target under 200ms.

Speed Index (SI)

How quickly the contents of a page are visibly populated. Target under 3.4s.

Time to Interactive (TTI)

Time until the page is fully interactive. Target under 3.8s.

Render-Blocking Resources

Scripts and styles that block initial rendering. Defer or inline critical paths.

Critical CSS

The minimum CSS required to render above-the-fold content. Inlined in <head>.

Lazy Loading

Deferring offscreen image and iframe loading until needed. Use loading="lazy".

Preload

Hint that tells browsers to fetch a resource early. Used for fonts and LCP images.

Preconnect

Hint that tells browsers to start the TCP+TLS handshake to a third-party origin early.

Technical SEO 36 terms

Schema Markup

Structured data added to pages so search engines can understand context. Use JSON-LD.

JSON-LD

Recommended schema format. Goes in a <script type="application/ld+json"> block.

Microdata

Older inline schema syntax. JSON-LD is now preferred.

Rich Results

Enhanced Google listings (stars, FAQ, recipes, etc.) driven by schema.

FAQPage Schema

Structured data for question-answer pages. Powers FAQ snippets in search.

HowTo Schema

Structured data for step-by-step guides. Used for tutorial-style pages.

BlogPosting Schema

Structured data for blog posts. Includes headline, author, datePublished, image.

Organization Schema

Site-level entity schema. Helps with knowledge panel eligibility.

Breadcrumb Schema

Structured data for breadcrumb trails. Surfaces in SERP listings.

Robots.txt

File at /robots.txt that tells crawlers which paths are off-limits.

XML Sitemap

List of indexable URLs submitted to search engines. Should be at /sitemap.xml.

Sitemap Index

A sitemap that references multiple sub-sitemaps. Required when you have over 50k URLs.

Canonical Tag

rel="canonical" link element that tells Google which URL is authoritative.

Hreflang

Tells Google which language and region a page targets. Critical for multilingual sites.

Meta Robots

Page-level directive that controls indexing and link following.

Noindex

Tells search engines to exclude a page from the index but still crawl it.

Nofollow

Link attribute that tells crawlers not to pass authority through that link.

X-Robots-Tag

HTTP header equivalent of meta robots. Used for non-HTML resources like PDFs.

Crawl Budget

How many URLs Google will crawl on your site over a period. Optimize by reducing waste.

Crawl Rate Limit

Max requests per second Google will make to your site. Influenced by server health.

Crawl Demand

How much Google wants to crawl your site. Driven by popularity and freshness.

Soft 404

A page that returns HTTP 200 but looks like a not-found. Google flags these as quality issues.

Redirect Chain

Multiple redirects in sequence. Each hop wastes crawl budget; keep under 2 hops.

301 Redirect

Permanent redirect. Passes nearly full link equity to the destination.

302 Redirect

Temporary redirect. Use sparingly — Google may not pass authority.

307 Redirect

Temporary redirect that preserves the request method. HTTP/1.1 spec.

308 Redirect

Permanent redirect that preserves the request method. Modern alternative to 301 for non-GET requests.

404 Error

Page not found. Important: 404s should return HTTP 404, not 200.

410 Gone

Permanently removed page. Tells Google to drop the URL faster than 404.

503 Service Unavailable

Use during planned downtime so Google doesn't deindex pages.

HTTPS

Encrypted HTTP. A confirmed Google ranking signal since 2014.

HSTS

HTTP header that forces HTTPS for all subsequent requests. Adds preload eligibility.

HTTP/2

Protocol upgrade with multiplexing and header compression. Faster than HTTP/1.1.

HTTP/3

Latest protocol over QUIC/UDP. Faster on lossy networks.

WebP

Modern image format. ~30% smaller than JPEG with same quality.

AVIF

Even more efficient image format. ~50% smaller than JPEG; growing browser support.

On-Page SEO 15 terms

Off-Page & Backlinks 15 terms

Content & E-E-A-T 15 terms

AI & AIO 17 terms

AI Overviews (AIO)

Google's AI-generated answer panel at the top of SERP. Replaced SGE in 2024.

Search Generative Experience (SGE)

Google's experimental AI search feature. Renamed AI Overviews in 2024.

AEO

Answer Engine Optimization. Adapting content for direct-answer surfaces.

GEO

Generative Engine Optimization. Optimizing for LLM-driven search like ChatGPT and Perplexity.

ChatGPT Search

OpenAI's web-grounded search inside ChatGPT. Cites sources from the open web.

Perplexity

AI-powered search engine that cites sources inline. Important new traffic surface in 2026.

Bing Copilot

Microsoft's AI search built on GPT. Drives meaningful query volume away from blue links.

Google Gemini

Google's flagship LLM, integrated across Search, Workspace, and the Gemini app.

Citation (AI Search) (AI citation)

Reference an AI assistant makes to your URL when answering a query. Your goal in AEO/GEO.

Snippet Optimization

Writing direct, scannable answers in the first 1-2 sentences of every section.

Cite-worthy Content

Content structured so AI assistants can lift clear, attributable claims directly.

Entity

A discrete object or concept (person, place, thing) that search engines model semantically.

Entity SEO

Optimizing for entities and relationships rather than raw keywords. Critical for AI-era ranking.

Knowledge Graph

Google's database of entities and their relationships. Powers knowledge panels.

Knowledge Panel

Right-side info box for entities. Driven by Knowledge Graph + Wikidata + structured data.

Zero-click Search

Searches that end on the SERP without a click. Increasing share due to AI Overviews.

Voice Search

Queries spoken into voice assistants. Tends to be longer, conversational.

Tools & Platforms 10 terms

Local SEO 6 terms

Analytics & UX 10 terms

HTTP & Web Standards 10 terms

UX & Accessibility 8 terms

See these signals in action on your site.

Free page-by-page atlookup audit — every glossary signal scored.

Run free audit