Cross-site request forgery (CSRF) is a type of security vulnerability that allows an attacker to trick a user into executing unwanted actions on a web application where they are authenticated. This can happen when a user is logged into a site, and the attacker sends a malicious request that the site processes as if it were a legitimate action from the user. To prevent CSRF attacks, web developers can implement various security measures, such as using anti-CSRF tokens, which are unique and unpredictable values included in requests. This ensures that the request is coming from a legitimate source, protecting users and their data from unauthorized actions.