Although we know it today by its short name—Doctor Faustus—the full title of the play when it was first printed in 1604 was The Tragicall Historie of Doctor Faustus. Now consider the title of the chapbook (as in, the Renaissance version of a paperback) that was Marlowe's probable source for his play: "The Historie of the Damnable Life, and Deserved Death, of Doctor Iohn Faustus." It's a mouthful, right? It seems that the name of this story in England just kept getting shorter and shorter as time passed, and boy are we grateful.
In any case, The Tragicall Historie of Doctor Faustus would have signaled the genre of this play—tragedy—to its audience right off the bat. But anyone who came into the playhouse expecting a typical Renaissance tragedy—you know, a story about the rise and fall of a king or some other VIP, usually incorporating lots of battle scenes and a dash of romance—would have been sorely disappointed.
No sooner has the Chorus opened its mouth than it warns us this isn't going to be that kind of tragedy. Nope, this is the story of a lowborn man (a commoner, you might say) who became a powerful scholar. This is a story about knowledge and learning, and how far one scholar was willing to go for it. In fact, most of it takes place not on a battlefield or in a royal court, but in a study. A study! Snooze.
At this point, the audience (and you, for that matter) may be feeling like they've been had. Where are the swords? Where's the romance?
But as the play progresses, we like to think that Marlowe called this one a tragedy because faithful viewers might reflect on how the lives of everyone—not just kings and queens, knights and maidens—can contain elements of tragedy and high drama. Just because Faustus wasn't a VIP doesn't mean his story isn't worth hearing.