Technical

301 redirect

Permanent redirect

A server-side permanent redirect that tells crawlers a URL has moved for good and that ranking signals should consolidate on the destination.

302 redirect

Found · Temporary redirect

A temporary redirect indicating the resource lives elsewhere for now; the original URL is expected to remain the canonical one.

307 redirect

Temporary Redirect

A temporary redirect that, unlike 302, guarantees the HTTP method and body are preserved; also the code browsers report for internal HSTS redirects.

308 redirect

Permanent Redirect

A permanent redirect equivalent to 301 for indexing purposes, but which forbids changing the HTTP method when following it.

Alt text

Alternative text

The alt attribute describing an image's content and function for screen readers, for cases where the image fails to load, and for image search.

AVIF

AV1 Image File Format

A modern image format based on the AV1 codec that generally compresses better than WebP, with wide but slightly less universal browser support.

Breadcrumb navigation

BreadcrumbList

A secondary navigation trail showing a page's position in the site hierarchy; with BreadcrumbList markup it can replace the URL line in search results.

Cache-Control

Caching headers

The HTTP header governing how browsers, CDNs and proxies store and revalidate a response, using directives such as max-age, s-maxage and stale-while-revalidate.

Chrome User Experience Report

CrUX · Field data

Google's public dataset of real-user performance measurements from opted-in Chrome users, and the official source of Core Web Vitals assessment.

Compression (gzip, Brotli, Zstandard)

Content-Encoding

Encoding text responses to reduce transfer size; Brotli typically beats gzip on HTML, CSS and JavaScript, with Zstandard now also supported by browsers.

Content Delivery Network

CDN

A distributed network of edge servers that caches and serves content close to users, reducing latency and offloading the origin.

Core Web Vitals

CWV

Google's set of three field-measured user experience metrics — LCP, INP and CLS — used as part of the page experience signals in ranking.

Cumulative Layout Shift

CLS

A Core Web Vital scoring unexpected visual movement of page content, computed from the largest burst of layout shifts; good is 0.1 or less at p75.

Edge SEO

Implementing SEO changes in CDN edge workers rather than the origin application, so fixes ship without touching the main codebase or release cycle.

ETag and conditional requests

If-None-Match · If-Modified-Since

A validator token identifying a specific version of a resource, allowing clients and crawlers to revalidate with a cheap 304 Not Modified response.

First Contentful Paint

FCP

The time from navigation start until the browser renders the first piece of DOM content; a diagnostic metric rather than a Core Web Vital.

First Input Delay

FID

The retired responsiveness Core Web Vital measuring only the delay before the browser began processing a page's first interaction; replaced by INP in March 2024.

Heading structure (H1-H6)

H1 · Headings

The hierarchy of HTML heading elements that conveys a document's outline to users, assistive technology and parsers.

HSTS

HTTP Strict Transport Security

A response header instructing browsers to only contact a host over HTTPS for a set period, eliminating the initial insecure request.

HTTP status codes

Response codes

Numeric codes in an HTTP response that tell crawlers how to treat a URL: 200 index it, 3xx follow the redirect, 404/410 drop it, 5xx come back later.

HTTP/2

h2

A binary, multiplexed version of HTTP that carries many concurrent requests over one TCP connection with header compression.

HTTP/3

QUIC

The version of HTTP that runs over QUIC on UDP, removing transport-level head-of-line blocking and speeding up connection setup.

HTTPS

TLS · SSL

HTTP over TLS, encrypting traffic between browser and server; a lightweight Google ranking signal since 2014 and a baseline expectation today.

Hydration

Rehydration

Attaching client-side JavaScript behaviour to server-rendered HTML so a static page becomes interactive.

Interaction to Next Paint

INP

A Core Web Vital measuring overall responsiveness as the latency of the worst (approximately) interaction on a page; good is 200 ms or less at p75.

Intrusive interstitial

Pop-up penalty

A pop-up or overlay that obscures the main content immediately after a user arrives from search, which Google's guidance discourages on mobile.

JSON-LD

JavaScript Object Notation for Linked Data

A W3C-standard JSON syntax for linked data, embedded in a `<script type="application/ld+json">` block; Google's recommended structured data format.

Largest Contentful Paint

LCP

A Core Web Vital measuring the render time of the largest image, video poster or text block visible in the viewport; good is 2.5 s or less at p75.

Lazy loading

Deferred loading

Deferring the download of offscreen images and iframes until they are near the viewport, using the native `loading="lazy"` attribute or IntersectionObserver.

Lighthouse

An open-source automated auditing tool in Chrome DevTools and PageSpeed Insights that runs lab tests for performance, accessibility, best practices and SEO.

Meta description

A page-level summary in a `<meta name="description">` tag, used as a candidate for the search snippet but not as a ranking factor.

Meta refresh redirect

Client-side redirect

A redirect implemented with `<meta http-equiv="refresh">` in the HTML; Google understands it but recommends server-side redirects instead.

Microdata

An HTML attribute-based syntax (itemscope, itemtype, itemprop) for embedding structured data directly in visible markup.

Mixed content

Insecure http subresources loaded by an https page; browsers block active mixed content and may upgrade or block passive content.

Mobile-first indexing

Google's practice of crawling, indexing and ranking based on the mobile version of a page; completed for all sites by mid-2024.

Page experience

Google's umbrella term for signals about how users perceive interacting with a page, including Core Web Vitals, HTTPS and absence of intrusive interstitials.

PageSpeed Insights

PSI

Google's public tool that shows CrUX field data and a Lighthouse lab audit for a URL and its origin, side by side.

Prefetch and speculation rules

rel=prefetch · Prerender

Hints that fetch or fully prepare resources for a likely next navigation at low priority, making the subsequent page load feel instant.

Preload

rel=preload

A resource hint that tells the browser to fetch a critical resource for the current page at high priority, before the parser would normally discover it.

Progressive enhancement

A build strategy that starts with working HTML and layers on CSS and JavaScript, so core content and navigation function without scripts.

RDFa

RDFa Lite

A W3C attribute syntax (vocab, typeof, property) for embedding RDF-based structured data in HTML; supported by Google but rarely used for new work.

Redirect chain

Redirect hop · Redirect loop

A sequence of two or more redirects between the requested URL and the final destination; each hop adds latency and risks signals being lost.

Render-blocking resources

Critical rendering path

Stylesheets and synchronous scripts in the head that must be downloaded and processed before the browser can paint anything.

Responsive web design

RWD

Serving the same HTML at one URL and adapting layout with CSS media queries and flexible units, Google's recommended mobile configuration.

Rich Results Test

Schema Markup Validator

Google's tool for checking whether a page's structured data qualifies for rich results, run against the rendered page.

Schema.org

Schema vocabulary

A collaborative vocabulary of types and properties for structured data on the web, founded by Google, Microsoft, Yahoo and Yandex in 2011.

Semantic HTML

Semantic markup

Using HTML elements according to their meaning — article, nav, main, table, time — rather than generic divs styled to look right.

Server-side rendering

SSR

Generating a page's full HTML on the server for each request, so crawlers and users receive complete markup without executing JavaScript.

Single-page application

SPA

An architecture where one HTML shell loads and JavaScript handles all subsequent routing and content updates without full page loads.

Site architecture

Information architecture · Site structure

How a site's URLs, navigation and internal links are organised into a hierarchy that users and crawlers can traverse efficiently.

Site name

The name Google displays for a website above the result URL, derived from WebSite structured data, og:site_name, the title element and other signals.

srcset and sizes

Responsive images

HTML attributes that offer the browser multiple image candidates at different widths so it can pick the smallest file that fits the layout and screen density.

Structured data

Schema markup

Machine-readable annotations on a page, usually Schema.org vocabulary in JSON-LD, that describe entities and make pages eligible for rich results.

Third-party scripts

Tag bloat

Externally hosted JavaScript such as analytics, tag managers, consent tools, chat widgets and ad code, which are a leading cause of poor INP and CLS.

Time to First Byte

TTFB

The interval between a navigation request starting and the first byte of the response arriving; a foundational input to LCP and a signal of server and network health.

Title tag

Title element · Title link

The `<title>` element describing a page, used as the primary input to the clickable headline in search results — which Google may rewrite.

URL structure

Slug · Permalink

The design of a site's URL paths: readable, stable, lowercase, hyphen-separated and free of unnecessary parameters or session identifiers.

Viewport meta tag

The `<meta name="viewport">` declaration that tells mobile browsers how to size and scale a page to the device screen.

Web accessibility (WCAG)

a11y

Designing and building so people with disabilities can use a site, guided by the W3C's Web Content Accessibility Guidelines.

Web font loading

FOIT · FOUT · font-display

The strategy for downloading and applying custom fonts; poor handling causes invisible text (FOIT), layout shift (FOUT) and slow LCP for text-led pages.

WebP

A Google-developed image format supporting lossy and lossless compression plus transparency and animation, typically 25-35% smaller than comparable JPEG or PNG.