The Same-Origin Policy is a security measure implemented in web browsers that restricts how documents or scripts from one origin can interact with resources from another origin. An origin is defined by the combination of the protocol (like HTTP or HTTPS), domain (like example.com), and port number. This policy helps prevent malicious activities, such as cross-site request forgery and data theft. When a web page tries to access resources from a different origin, the browser blocks the request unless specific permissions are granted. This ensures that sensitive data remains protected and that scripts cannot manipulate content from other sites without authorization, maintaining user security and privacy.