An authentication token is a digital credential used to verify a user's identity when accessing applications or online services. Instead of requiring a password for every action, the system issues a unique token after the initial login, which serves as proof of identity for subsequent requests. These tokens are often temporary and can be stored on devices or browsers. If an authentication token is intercepted or stolen, unauthorized users may gain access to the associated account or data. Tokens are a core part of modern security protocols, enabling secure and seamless user experiences.