token
Like a wristband that proves you passed the gate, a token is a short-lived proof that a user or app may do something.
A service creates a token after someone signs in or after your server swaps an API key for limited permission. It is proof you can show again without sending a password each time.
Tokens matter because they can expire or be revoked, which limits damage if stolen. They let mobile apps stay signed in and call services without storing sensitive details.
In practice: a token looks like a long jumble, often with dots. The app sends it with each request, a message to a service, and the service checks it before doing the work. On phones it is kept in secure storage, the device’s locked drawer.