Is cheesecake a cake or a pie?
Since it's round and has layers (custard and base), some say cake; others cite the filling and bottom crust and say it's pie. Some prefer the definition of tart, which "The Oxford Companion to Food" describes as "a flat, baked item consisting of a base of pastry ... with a sweet or savoury topping not covered with a pastry lid."
However, I like the other most common answer: It's a custard. It's usually made from a batter of cream cheese or ricotta and eggs and baked in a water bath like pudding or flan.
MCT