A canopy is a roof-like covering for a bed, made of fabric. A lot of little girls dream of having a four-poster bed with a ruffled canopy.
Any fabric cover that acts as a roof can be called a canopy, and so can something resembling such a covering, like a canopy of leaves created by trees. The Greek word that's at the root of canopy is konopeion, which means "Egyptian couch with mosquito curtains." The Old French conope, which evolved into today's canopy, originally meant "bed-curtain."