A JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties. It consists of three parts: a header, a payload, and a signature. The header typically indicates the type of token and the signing algorithm used. The payload contains the claims, which can include user information and permissions. JWTs are commonly used for authentication and information exchange in web applications. They allow servers to verify the token's authenticity and ensure that the claims have not been tampered with. This makes JWTs a popular choice for securing APIs and managing user sessions.