The “bearer” prefix indicates the token is a “bearer” type token, as defined in RFC6750. As opposed to, for example, a “mac” token type.

The bearer token can be a JWT, but can also be a different format of bearer token as long as it conforms to the requirements in the spec (ie, only certain characters are allowed).

A “bearer” token means whoever has the token has authorization to perform the action. (Section 1.2 of the RFC goes into more details.)