Tartuffe. Sounds like some kind of fancy dessert, no? Well, it isn't. It is, however, the name of a character in the play. Now, let's take a look at the list of characters. Ah! There it is. If we were French, we'd see Tartuffe, faux dèvot, which is basically just an old French way of saying "hypocrite." (It literally means "fake deeply religious person.") So we can assume that the play is about some guy named Tartuffe who's a hypocrite.
OK, that's pretty good, but this begs the question: what exactly is a hypocrite? It's one of those words, like ironic, that gets tossed around a lot, and so loses some of its meaning in the process. In general, it's someone who doesn't practice what they preach; in this particular case, it's, well, someone who really doesn't practice what he preaches. Tartuffe himself doesn't get the most stage time of all the characters, but he's present throughout. For better or for worse, he's the mover and the shaker, the one who gets people talking and, in some cases, emptying out their wallets.