An OAuth token is a secure digital key used to grant applications limited access to your online accounts without sharing your password. When you sign in to a new app using your Google or Facebook account, OAuth tokens let the app access specific data (like your email or contacts) for a set period. This process keeps your password private and allows you to control what information each app can see or use. OAuth tokens are widely used to improve security and user experience by enabling safe, password-free connections between services.