The term 'doggy door' is a phrase used to describe a small door or FLAP installed in a wall or exterior door of a house that allows a pet, usually a dog, to enter and exit the house without having to open the door for them. The crossword solution for this term is 'FLAP, ' which is a piece of material that hangs loose at one side and is attached at the other side, allowing it to swing back and forth.