A favicon is the small icon a browser uses to represent a site in places like tabs, bookmarks, history lists, and, in some browsers, the address bar. The name is short for "favorite icon," a reference to the Favorites feature in early Internet Explorer.
Favicons first appeared in Internet Explorer 5, released in March 1999. In that first implementation, the browser looked for a file named favicon.ico in the root of a website. The icon was primarily associated with bookmarks and Favorites, and Internet Explorer could also show it next to the URL when a page had been bookmarked. That behavior made the root-level favicon.ico file a de facto web convention long before the feature was formally standardized.
As other browsers adopted site icons, the feature became more flexible. Authors were no longer limited to a single root file, and browsers increasingly supported declaring icons in HTML with <link rel="icon">. That made it possible to provide different formats, MIME types, and sizes so the browser could choose the best match for the current context. The older shortcut icon form still appears on legacy pages, but the standard relation is simply icon.
The favicon also outgrew the idea of a single 16x16 image. Sixteen pixels remained the classic tab size, but authors increasingly shipped larger icon assets for higher-density displays and other browser or operating-system contexts. ICO files could bundle multiple raster sizes in one file, and modern browsers added support for formats such as PNG. Some browsers also support SVG favicons, though support still varies by browser and context.
Mobile devices introduced a related but separate branch of this history. On iPhone and iPad, Apple added Home Screen icons for saved websites through the non-standard apple-touch-icon link relation, or by looking for apple-touch-icon.png at the site root. Those icons are not selected the same way as ordinary favicons, and iOS has long treated them as a distinct feature for Web Clips rather than as standard rel="icon" resources.
Installable web apps added another layer. Progressive Web Apps use the Web App Manifest, where an icons array describes the images used for installation, launchers, splash screens, and operating-system surfaces. These manifest icons are closely related to a site's visual identity, but they are technically separate from the browser tab favicon.
Today, many sites publish several kinds of icons at once: a favicon for browsers, Apple touch icons for iOS Home Screen saves, and manifest icons for installed web apps. They are often generated from the same source artwork, but they serve different technical purposes.
What has stayed constant is the job itself. A favicon is still a tiny piece of interface design that helps people recognize where they are at a glance. It remains one of the smallest assets on a site, but also one of the most persistent.