JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed. JWTs can be signed using a secret (with theĀ HMACĀ algorithm) or a public/private key pair usingĀ RSAĀ orĀ ECDSA.

From: jwt.io

This is a great e-book on the entire OAuth standard that touches on JWTs.