Fly can refer to any of the following things:

• A fly (plural flies) is any species of insect of the order Diptera.

• A fly is a lure, used in angling, with materials such as feathers or cotton thread, tied to look like a real fly.

• Flies in trousers are a zipped, velcroed or buttoned opening, desined to allow men ease of access when dressing and undressing, as well as urinating.

• Flies in a theatre refers to the fly tower over the stage or to a storage are to the side of the stage.

• In baseball, a fly is a ball that is hit into the air. See: fly ball.

• The Fly is the title of two horror movies:
  • The Fly (1958), directed by Kurt Neumann, and
  • The Fly (1986), directed by David Cronenberg, which is a remake of the first one.

In the English language, fly means:

• As a verb, fly means to travel through air in the act of flight, like a bird or aeroplane, or to travel on or pilot an aircraft.

• Fly is also a slang term, meaning "cool" or "hip".