Userscripts are small pieces of JavaScript code that allow users to customize the way web pages look and function. They can modify existing content, add new features, or automate repetitive tasks on websites. Userscripts are typically run in web browsers using extensions like Tampermonkey or Greasemonkey. These scripts are often shared within online communities, enabling users to enhance their browsing experience. By installing a userscript, individuals can tailor websites to better suit their needs, improving usability and efficiency while navigating the internet.