Search & indexing
Terms that describe how pages identify themselves and how search engines discover, interpret and index them.
Page title
The title declared in a page’s HTML. It appears in the browser tab and is one of the main sources a search engine may use when presenting the page in results.
Why it matters: A useful title helps people and search engines distinguish one page from another. It should describe the page rather than act as a list of keywords.
Meta description
A short description supplied in a page’s HTML metadata.
Why it matters: Search engines may use it when constructing a search-result snippet, although they can choose different text from the page when that better answers a particular search.
Canonical URL
The address a page identifies as its preferred or main version when substantially equivalent content may be available at more than one URL.
Why it matters: A coherent canonical system helps consolidate duplicate URL variants and makes the intended page identity clearer to search engines.
Indexing
The process by which a search engine stores and organises information about a page so that the page can potentially appear in search results.
Why it matters: Being crawlable is not the same thing as being indexed, and being indexed does not guarantee a particular ranking.
noindex
A robots directive asking search engines not to keep a page in their search index.
Why it matters: It is useful for genuinely private or low-value result pages, but an accidental noindex instruction on an important public page can prevent that page appearing in search.
robots.txt
A public text file at the root of a website that gives automated crawlers instructions about which areas they may crawl.
Why it matters: It can guide well-behaved crawlers and point them towards a sitemap, but it is not a security or access-control mechanism.
Sitemap
A machine-readable list of URLs that a website wants search engines to discover and process.
Why it matters: A sitemap can make discovery and maintenance clearer, especially on larger sites, but a small site does not become invisible merely because a sitemap is absent.
Redirect
A server response that sends a visitor or crawler from one URL to another.
Why it matters: Redirects are important when addresses change. Clean permanent redirects can preserve useful routes; unnecessary chains and loops create delay and ambiguity.
Structured data
Machine-readable information that describes the meaning and relationships of content on a page using an agreed vocabulary such as Schema.org.
Why it matters: Accurate structured data can help systems interpret a page, but it must reflect visible truthful content and does not guarantee a special search result.
JSON-LD
A JSON-based format commonly used to add structured data to a web page.
Why it matters: It lets a site describe entities and relationships cleanly without mixing those machine-readable properties into visible page markup.
Page structure & accessibility
Terms connected with semantic page structure and some of the foundations that help people and assistive technology understand a page.
H1
An HTML level-one heading, normally used for the principal heading of a page.
Why it matters: A clear primary heading helps readers, assistive technology and other systems understand what the page is principally about.
Heading hierarchy
The ordered use of heading levels to describe sections and subsections of a page.
Why it matters: Logical headings make long pages easier to scan and give assistive technology a more useful map of the content.
Alternative text
Text associated with an image that communicates the image’s useful meaning when the image cannot be seen or is not available.
Why it matters: Meaningful images need useful text alternatives. Purely decorative images are normally better represented by an intentionally empty alternative rather than a description that adds noise.
Accessible name
The name assistive technology can use to identify a control, link, image or other interface element.
Why it matters: A field or button can look obvious visually but still be difficult to understand if its accessible name is missing or misleading.
Document language
The language declared for a web page, usually through the HTML `lang` attribute.
Why it matters: A correct language declaration helps browsers and assistive technology pronounce and process text appropriately.
Viewport
The visible browser area used to lay out a page. Mobile pages commonly include viewport metadata so the layout follows the device width.
Why it matters: Correct viewport behaviour is one foundation of a usable responsive page, although it does not by itself prove that the mobile layout is good.
iframe
An HTML element that embeds another web page or document inside the current page.
Why it matters: Iframes are useful for some maps, videos and third-party tools, but they add another document boundary and need appropriate naming and careful third-party consideration.
Technical foundations
Terms describing web delivery, browser behaviour, caching, external resources and resilient page construction.
HTTPS
The encrypted form of HTTP used to carry web traffic securely between a browser and a website.
Why it matters: HTTPS protects traffic in transit and helps visitors know they are connected to the intended site. Certificate or redirect problems can undermine that protection.
HTTP status
A numeric response code from a web server describing what happened to a request, such as 200 for success, 301 for a permanent redirect or 404 for a missing page.
Why it matters: Correct status codes help browsers, search engines and monitoring systems understand whether a page exists, moved or failed.
Compression
Reducing the number of bytes sent across the network for text-based assets such as HTML, CSS or JavaScript.
Why it matters: Appropriate HTTP compression can reduce transfer time without changing the underlying content.
Cache header
An HTTP instruction that helps browsers and intermediary systems decide whether and for how long a response may be reused.
Why it matters: Good caching can avoid unnecessary repeat downloads, while sensitive or frequently changing responses may need stricter cache rules.
Third-party script
JavaScript loaded from a domain controlled by another service or organisation.
Why it matters: Third-party code can provide useful services, but it also adds performance, resilience and sometimes privacy considerations that are worth understanding.
Responsive image
An image delivered with alternatives so a browser can choose a suitable file for the available display size and device.
Why it matters: Responsive image delivery can preserve visual quality while avoiding unnecessarily large downloads on smaller screens.
Performance
Terms used when describing how quickly and steadily a page responds and becomes usable.
Core Web Vitals
Google’s current set of user-experience performance measures centred on loading speed, interaction responsiveness and visual stability.
Why it matters: They are most useful when interpreted from real-user data over time rather than treated as a one-off score or the sole measure of website quality.
Largest Contentful Paint (LCP)
A Core Web Vital measuring how long it takes the largest relevant piece of visible content to appear.
Why it matters: LCP is one way of describing perceived loading speed. Images, fonts, server response and render-blocking resources can all influence it.
Interaction to Next Paint (INP)
A Core Web Vital describing how responsive a page feels when people interact with it.
Why it matters: Long-running JavaScript and busy main-thread work can make controls feel slow even after the page initially appears.
Cumulative Layout Shift (CLS)
A Core Web Vital describing unexpected movement of visible page content while the page is being used.
Why it matters: Reserved image dimensions, stable fonts and carefully loaded interface elements help prevent distracting layout jumps.
Time to First Byte (TTFB)
The time between making a request and receiving the first byte of the server response.
Why it matters: TTFB can reveal part of the delay before the browser has enough response data to begin useful rendering, but it is only one part of overall page performance.