OAuth2 is an authorization framework that allows third-party applications to access a user's data without sharing their password. It enables users to grant limited access to their information on one service to another service, ensuring security and privacy. This is commonly used in scenarios like logging into a website using your Google or Facebook account. The process involves several roles: the resource owner (user), the client (application requesting access), and the authorization server (service that grants access). Users authenticate with the authorization server, which then provides an access token to the client, allowing it to access the user's data securely.