B-actor

a B-actor is an actor hired to act in B-movies. B-actors are generally less well-known but not necessarily less talented than top actors. Many famous movie stars began their careers as B-movie actors, such as John Wayne. Others, such as Bruce Campbell, who incorporated the term into the title of his auto-biography, have embraced it

An actor/actress who was popular for a brief period of time but stooped staring in major works.

They are essestially the opposite of an "A-list actor" which is somebody at the hight of their popularity in Hollywood