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Glossary

Website Performance

Website performance describes how quickly and reliably a website loads, responds, and delivers useful content to users.

Terms

Bottleneck A performance bottleneck is the part of a system that most significantly limits how quickly the website can complete a task or present useful content. Caching Caching stores previously retrieved content or resources so they can be reused without repeating the complete request and delivery process. Code Splitting Code splitting divides JavaScript into smaller pieces so the browser can load only the code needed for the current page or interaction. Compression Compression reduces the amount of data transferred between a server and browser by encoding resources more efficiently during delivery. Content Delivery Network (CDN) A content delivery network is a distributed network of servers used to deliver website resources from infrastructure closer to the people requesting them. Critical CSS Critical CSS is the minimum set of styles required to render the important content visible during the initial page load. Critical Rendering Path The critical rendering path is the sequence of work a browser performs to turn the resources needed for a page into visible content. Image Optimization Image optimization reduces unnecessary image data and loading work while preserving the visual quality required for the image's purpose. JavaScript Bundle A JavaScript bundle is a browser-delivered file containing JavaScript code combined from multiple modules or source files. Lazy Loading Lazy loading delays non-critical resources until they are likely to be needed instead of loading everything during the initial page request. Main Thread The main thread is the browser thread responsible for much of the JavaScript, layout, style, and rendering work required to run a web page. Page Weight Page weight describes the total amount of data transferred to load a web page and the resources required by it. Perceived Performance Perceived performance describes how fast, stable, and responsive a website feels to the person using it rather than how long every background resource takes to finish loading. Render Blocking Render blocking occurs when a browser must wait for a resource or task before it can continue rendering visible page content. Resource Hint A resource hint gives the browser additional information that can help it prepare for or load an important resource earlier. Third-Party Script A third-party script is JavaScript provided or controlled by an external service and embedded into a website to provide additional functionality. Web Font A web font is a font file downloaded by the browser to display typography that may not already be installed on the user's device. Website Performance Website performance describes how quickly and reliably a website loads, becomes usable, responds, and presents content during real use.