What is the meaning of 'Cages aux Folles'?

Bird Cage

"La cage aux folles" means literally "the cage of madwomen." "Folles," however, is also a slang term for effeminate homosexuals (queens). The expression does not really mean "birdcage," but it is impossible to translate effectively in one catchy phrase.

It may help to realize that "bird" is British slang for woman, like "chick".