Technical SEO terms

Crawling, indexing, redirects, canonicals, sitemaps, structured data and page speed. 55 terms, each with what it means, why it matters for SEO and what to do about it.

301 redirect

A 301 redirect permanently sends visitors and search engines from one URL to another and tells Google the new URL should be indexed.

302 redirect

A 302 redirect temporarily sends visitors to another URL while telling search engines to keep the original URL indexed.

404 error

A 404 error is the HTTP status a server returns when a requested page does not exist. It is normal, but broken links to 404s are worth fixing.

5xx server errors

5xx server errors are HTTP status codes meaning the server failed to handle a request. Persistent ones make Google crawl less and drop pages.

Canonical tag

A canonical tag is a link element that tells search engines which URL is the main version of a page when duplicates exist.

CDN (content delivery network)

A CDN (content delivery network) is a network of servers around the world that caches and serves your site from locations close to each visitor.

Client-side rendering (CSR)

Client-side rendering (CSR) sends a near-empty HTML page and builds the content in the browser with JavaScript, which crawlers must run to see it.

Core Web Vitals

Core Web Vitals are Google’s three metrics for real-world page experience: Largest Contentful Paint, Interaction to Next Paint and Cumulative Layout Shift.

Crawl budget

Crawl budget is the set of URLs Google can and wants to crawl on a site. It only becomes a constraint on very large or fast-changing sites.

Crawl depth

Crawl depth is how many clicks a page is from the homepage. Deep pages are found and crawled less often than shallow ones.

Cumulative Layout Shift (CLS)

Cumulative Layout Shift (CLS) is a Core Web Vital that measures how much content moves unexpectedly while a page is used. Good is 0.1 or less.

Duplicate content

Duplicate content is the same or very similar content available at more than one URL, on one site or across sites. Google picks one version to show.

Faceted navigation

Faceted navigation lets visitors filter a list by attributes such as size, colour or price, and can create huge numbers of crawlable URLs.

Hreflang

Hreflang is an annotation that tells search engines which language or regional version of a page to show to which searchers.

HSTS (Strict-Transport-Security)

HSTS is a response header that tells browsers to only connect to a site over HTTPS, so they never load it over insecure HTTP.

HTML sitemap

An HTML sitemap is a normal web page that links to a site’s main sections and pages, mainly to help visitors and crawlers navigate.

HTTP status codes

HTTP status codes are three-digit numbers a server returns with each response to say whether a request worked, moved or failed.

HTTPS

HTTPS is the encrypted version of HTTP. It protects data between browser and site, and Google uses it as a lightweight ranking signal.

Index bloat

Index bloat is when a search engine indexes many more of a site’s pages than it should, most of them low-value, duplicate or unintended URLs.

IndexNow

IndexNow is an open protocol that lets a site notify search engines such as Bing and Yandex the moment a URL is added, changed or deleted.

Interaction to Next Paint (INP)

Interaction to Next Paint (INP) is a Core Web Vital that measures how quickly a page responds to clicks, taps and key presses. Good is 200 ms or less.

JavaScript SEO

JavaScript SEO is the work of making sure search engines can crawl, render and index content and links that a site builds with JavaScript.

JSON-LD

JSON-LD is a JSON-based format for structured data, placed in a script tag. It is the format Google recommends for schema markup.

Lang attribute

The lang attribute declares the language of a page’s content, usually on the <html> element, for browsers, screen readers and translation tools.

Largest Contentful Paint (LCP)

Largest Contentful Paint (LCP) is a Core Web Vital that measures when the largest image or text block in the viewport appears. Good is 2.5 seconds or less.

Lazy loading

Lazy loading delays loading images, iframes or other content until they are about to scroll into view, which speeds up the first load of a page.

Lighthouse

Lighthouse is Google’s open-source tool that tests a page in a lab and scores its performance, accessibility, best practices and SEO.

Log file analysis

Log file analysis is reviewing your server’s access logs to see exactly which URLs search engine bots requested, when and with what result.

Mixed content

Mixed content is when an HTTPS page loads images, scripts or other files over insecure HTTP. Browsers block or upgrade much of it.

Mobile-first indexing

Mobile-first indexing means Google crawls and indexes the mobile version of your pages and uses it for ranking, on mobile and desktop alike.

Nofollow

Nofollow is a link attribute or meta directive asking search engines not to follow or credit links. Google treats it as a hint.

Noindex

Noindex is a robots directive, set in a meta tag or HTTP header, that tells search engines not to show a page in search results.

Orphan page

An orphan page is a page with no internal links pointing to it, so visitors and crawlers cannot reach it by browsing the site.

Page speed

Page speed is how quickly a page loads, shows its content and responds to input. Google measures it mainly through Core Web Vitals.

PageSpeed Insights

PageSpeed Insights is Google’s free tool that shows a page’s real-user Core Web Vitals and a Lighthouse lab test with suggestions, for mobile and desktop.

Pagination

Pagination splits a long list of items, such as products or articles, across a series of numbered pages, each with its own URL.

Redirect chain

A redirect chain is when a URL redirects to another URL that redirects again, so it takes two or more hops to reach the final page.

Redirect loop

A redirect loop is when redirects send a URL back to itself, so the page never loads and browsers show a too-many-redirects error.

Render-blocking resources

Render-blocking resources are CSS and JavaScript files that the browser must download and process before it can show any of the page.

Rich results

Rich results are Google search results with extra visual features, such as star ratings, prices or event dates, usually powered by structured data.

Robots.txt

Robots.txt is a plain-text file at the root of a site that tells crawlers which URLs they may and may not request.

Schema markup

Schema markup is structured data that uses the schema.org vocabulary to describe things on a page, such as products, articles and businesses.

Security headers

Security headers are HTTP response headers that tell browsers how to handle a site’s content safely, blocking common attacks.

Server-side rendering (SSR)

Server-side rendering (SSR) builds a page’s full HTML on the server for each request, so browsers and crawlers get the content in the first response.

Site architecture

Site architecture is how a website’s pages are organised and linked together, which shapes how people and search engines find and value them.

Site health score

A site health score is a single number, usually 0 to 100, that an SEO audit tool calculates from the technical issues found when it crawls a site.

Soft 404

A soft 404 is a page that returns a 200 success code but looks like an error or empty page, so Google treats it as not found.

Structured data

Structured data is code in a standard format that describes a page’s content to search engines, making it eligible for rich results.

Thin content

Thin content is a page with little or no useful content of its own, such as near-empty pages, copied text or doorway pages.

Time to First Byte (TTFB)

Time to First Byte (TTFB) is the time from requesting a page until the first byte of the response arrives. It sets the floor for every other speed metric.

URL parameters

URL parameters are key-value pairs after a ? in a URL, used for tracking, sorting, filtering and pagination. Each variation can look like a new page.

User agent

A user agent is the software making a web request, identified by a user-agent string such as Googlebot’s that servers and robots.txt can read.

Viewport meta tag

The viewport meta tag tells mobile browsers how to size and scale a page. Without it, phones show a shrunken desktop layout.

X-Robots-Tag

X-Robots-Tag is an HTTP response header that gives search engines robots directives such as noindex, including for PDFs and images.

XML sitemap

An XML sitemap is a file that lists the URLs you want search engines to crawl and index, with optional last-modified dates.