Gargoyle is a fearsome word for a monster. Fortunately, it's not a real monster. It's a grotesque carved beast sticking out from the gutter of a building, especially in Gothic architecture.
If you've ever seen a statue of an ugly beast coming out of the side of the building, you've seen a gargoyle. There aren't a lot of pretty, friendly looking gargoyles in the world; they usually look frightening, strange, and grotesque (which is kind of a mix of really ugly and kind of bizarre). Gargoyles have a couple purposes. For one thing, they're part of the drainage system that keeps the building from flooding. Secondly, they're so nasty-looking that they should scare off evil spirits who would do harm to the building or the people inside. Too much water and too much evil are both bad for a building.