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Definition
A JSON Web Token, or JWT, is a compact, digitally signed token that carries information between two parties. It can include details such as a user ID, token expiration time, and permissions, and is often used in authentication and authorization systems.

Why it matters
JWTs matter because they give applications a standard way to pass trusted information between services. They are commonly used in login systems, APIs, and single sign-on flows to confirm identity or access rights.

Example use case
A user signs in to a web app. The system issues a JWT that includes the user’s ID and session details, allowing the app to recognize the user during future requests.