As in "classically trained Shakespearian actor". These actors (male and female), usually Brits, have had some serious training--often a stint at the Royal Shakespeare Company--and so have developed redoubtable acting skills. Of course, they won't necessarily limit themselves to Shakespeare -- or even to theater. It's entirely possible for these people to do comedy, appear in major action movies and even enter Large Ham territory at times (see, for instance, Brian Blessed).