A URI scheme is a component of a Uniform Resource Identifier (URI) that specifies how the resource can be accessed. It typically appears at the beginning of a URI and indicates the protocol or method used to retrieve the resource. Common URI schemes include http, https, ftp, and mailto, each serving different purposes for accessing web pages, files, or email. URI schemes help browsers and applications understand how to handle the resource. For example, when a user clicks a link starting with https, the browser knows to use the secure Hypertext Transfer Protocol to fetch the web page. This standardization allows for seamless navigation and interaction across the internet.