a piece of something thin, such as cloth, paper, or metal, hinged or attached only on one side, that covers an opening or hangs down from something.
the flap of the envelope
a movement of a wing or an arm from side to side or up and down.
the surviving bird made a few final despairing flaps
a state of agitation; a panic.
they're in a flap over who's going to take Henry's lectures