Technical SEO & Web Performance Glossary

The percentage of visitors who navigate away from a site after viewing only one page, without taking any action.

The percentage of website visitors who complete a desired action, such as making a purchase, signing up, or filling out a form.

The process of storing copies of data in a temporary storage location so that future requests can be served faster.

A technique that breaks JavaScript bundles into smaller chunks that can be loaded on demand, improving initial page load performance.

The sequence of steps the browser takes to convert HTML, CSS, and JavaScript into pixels on the screen.

A public dataset of real user experience data from millions of websites, collected from Chrome users who have opted in to usage statistic reporting.

A geographically distributed network of servers that work together to provide fast delivery of internet content by serving it from locations closer to users.

A set of three metrics defined by Google that measure the loading performance, interactivity, and visual stability of a web page.

The specific performance targets that define whether a Core Web Vitals metric is considered Good, Needs Improvement, or Poor.

A Core Web Vital that measures visual stability by quantifying how much page content unexpectedly shifts during loading.

The number of pages a search engine crawler will fetch from a site within a given window, determined by crawl rate and crawl demand.

Instructions delivered via robots.txt, meta robots tags, or X-Robots-Tag headers that tell search engine crawlers what to crawl, index, or follow.

Periods when a website or service is unavailable or not functioning properly for users.

In Google Analytics 4, the percentage of sessions that were engaged sessions, where users actively interacted with the page.

Performance metrics collected from real users in production environments, as opposed to lab data collected in controlled testing conditions.

A deprecated metric (formerly a Core Web Vital) that measures the time from when a user first interacts with your page to when the browser can respond to that interaction.

A performance metric that measures the time from when the page starts loading to when any part of the page's content is rendered on screen.

A web analytics service by Google that tracks and reports website traffic, user behavior, and conversion data.

A free tool from Google that helps website owners monitor, maintain, and troubleshoot their site's presence in Google Search results.

Hypertext Transfer Protocol Secure, an extension of HTTP that uses encryption to secure communication between browser and server.

The process of reducing image file sizes and improving delivery to enhance web performance without significantly affecting visual quality.

A Core Web Vital that assesses page responsiveness by measuring the latency of all user interactions throughout the page lifecycle.

The process by which search engines store and organize web content so it can be retrieved and displayed in search results.

The time the browser spends parsing, compiling, and executing JavaScript code, which can block the main thread and delay interactivity.

The time delay between a user action and the system's response, often referring to network delay in web performance.

A design pattern that defers the loading of non-critical resources until they are needed, typically when they enter the viewport.

Performance metrics collected in controlled testing environments using tools like Lighthouse, as opposed to field data from real users.

A Core Web Vital that measures how long it takes for the largest content element visible in the viewport to render.

An open-source automated tool by Google for auditing the quality of web pages, measuring performance, accessibility, SEO, and more.

The primary thread in a browser where JavaScript execution, DOM manipulation, and rendering operations occur.

The process of removing unnecessary characters from code without changing its functionality, reducing file size for faster downloads.

A web design approach where pages are optimized for viewing and interaction on mobile devices with smaller screens and touch interfaces.

A metric that counts the total number of times a specific page on a website has been viewed by visitors.

Analytics tools designed to collect website data without tracking individual users, using cookies, or requiring consent banners.

A set of limits on performance metrics that a website should not exceed, used to maintain fast user experiences.

A browser hint that tells the browser to fetch a resource early because it will be needed soon, improving load performance.

A set of signals that Google uses to measure how users perceive the experience of interacting with a web page beyond its pure information value.

A Google tool that analyzes web page content and provides suggestions to make pages faster, combining both lab and field data.

Resources that prevent the browser from rendering page content until they are fully downloaded and processed.

A type of performance monitoring that captures and analyzes data from actual user sessions visiting a website.

A text file at the root of a website that tells search engine crawlers which pages or files they can or cannot request from the site.

A web design approach that makes pages render well on all screen sizes and devices, from desktop monitors to mobile phones.

A group of user interactions with a website that take place within a given time frame, typically ending after 30 minutes of inactivity.

The time it takes for a server to respond to a request from a browser, measured from request initiation to receiving the first byte of response.

A type of performance monitoring that uses automated scripts to simulate user interactions and measure performance in controlled conditions.

A file that lists all the URLs of a website that should be indexed by search engines, helping crawlers discover content.

A performance metric that measures how quickly content is visually displayed during page load.

A digital certificate that authenticates a website's identity and enables an encrypted connection between a web server and browser.

JavaScript code loaded from external domains, such as analytics, ads, social widgets, and other embedded services.

A performance metric that measures the time between the request for a resource and when the first byte of a response begins to arrive.

A lab metric that measures how long it takes a page to become fully interactive, where the user can reliably interact with the page.

A lab metric that measures the total amount of time the main thread was blocked long enough to prevent input responsiveness.

A metric that counts the number of distinct individuals who visit a website during a specific time period, regardless of how many times they visit.

A type of monitoring that continuously checks whether a website or service is available and responding to requests.

A Google Search Console feature and API that returns a per-URL report on indexing status, last crawl date, mobile usability, structured data, canonical assignment, and blocking issues.

The speed at which web pages are downloaded and displayed in the user's browser, and how responsive they are to user interaction.

A set of metrics from Google designed to measure the quality of user experience on the web, including but not limited to Core Web Vitals.

An automated program that systematically browses the web to discover and index content for search engines.