A bookmarklet is a small JavaScript program stored as a URL within a web browser's bookmarks. When clicked, it performs a specific function on the current webpage, such as changing the page's appearance, extracting information, or interacting with web services. Bookmarklets are easy to create and can enhance browsing by adding custom features without needing to install additional software. To use a bookmarklet, simply drag it to your bookmarks bar or save it as a bookmark. When you want to activate it, just click on the bookmarklet while visiting a webpage. This makes it a convenient tool for users looking to streamline their online experience.