JSON Web Tokens (JWT) are a compact and secure way to transmit information between parties as a JSON object. They are commonly used for authentication and information exchange in web applications. A JWT consists of three parts: a header, a payload, and a signature, which together ensure the integrity and authenticity of the data. When a user logs in, a server generates a JWT that includes user information and signs it with a secret key. This token is then sent to the client, which can use it to access protected resources without needing to log in again, enhancing user experience and security in applications like web services and APIs.