Source : Webster's Revised Unabridged Dictionary (1913)

Flap \Flap\, v. t. [imp. & p. p. {Flapped}; p. pr. & vb. n.
   {Flapping}.] [Prob. of imitative origin; cf. D. flappen, E.
   flap, n., flop, flippant, fillip.]
   1. To beat with a flap; to strike.

            Yet let me flap this bug with gilded wings. --Pope.

   2. To move, as something broad and flaplike; as, to flap the
      wings; to let fall, as the brim of a hat.

   {To flap in the mouth}, to taunt. [Obs.] --W. Cartwright.

Flap \Flap\, v. i.
   1. To move as do wings, or as something broad or loose; to
      fly with wings beating the air.

            The crows flapped over by twos and threes. --Lowell.

   2. To fall and hang like a flap, as the brim of a hat, or
      other broad thing. --Gay.

Flap \Flap\, n. [OE. flappe, flap, blow, bly-flap; cf. D. flap,
   and E. flap, v.]
   Anything broad and limber that hangs loose, or that is
   attached by one side or end and is easily moved; as, the flap
   of a garment.

         A cartilaginous flap upon the opening of the larynx.
                                                  --Sir T.
                                                  Browne.

   2. A hinged leaf, as of a table or shutter.

   3. The motion of anything broad and loose, or a stroke or
      sound made with it; as, the flap of a sail or of a wing.

   4. pl. (Far.) A disease in the lips of horses.

   {Flap tile}, a tile with a bent up portion, to turn a corner
      or catch a drip.

   {Flap valve} (Mech.), a valve which opens and shuts upon one
      hinged side; a clack valve.

Source : WordNet®

flap
     n 1: any broad thin and limber covering attached at one edge;
          hangs loose or projects freely; "he wrote on the flap of
          the envelope"
     2: an excited state of agitation; "he was in a dither"; "there
        was a terrible flap about the theft" [syn: {dither}, {pother},
         {fuss}, {tizzy}]
     3: the motion made by flapping up and down [syn: {flapping}, {flutter},
         {fluttering}]
     4: a movable piece of tissue partly connected to the body
     5: a movable airfoil that is part of an aircraft wing; used to
        increase lift or drag [syn: {flaps}]
     [also: {flapping}, {flapped}]

flap
     v 1: move in a wavy pattern or with a rising and falling motion;
          "The curtains undulated"; "the waves rolled towards the
          beach" [syn: {roll}, {undulate}, {wave}]
     2: move noisily; "flags flapped in the strong wind"
     3: move with a thrashing motion; "The bird flapped its wings";
        "The eagle beat its wings and soared high into the sky"
        [syn: {beat}]
     4: move with a flapping motion; "The bird's wings were
        flapping" [syn: {beat}]
     5: make a fuss; be agitated [syn: {dither}, {pother}]
     6: pronounce with a flap, of alveolar sounds
     [also: {flapping}, {flapped}]

Source : Free On-Line Dictionary of Computing

FLAP
     
        A {symbolic mathematics} package for {IBM 360}.
     
        ["FLAP Programmer's Manual", A.H. Morris Jr., TR-2558 (1971)
        US Naval Weapons Lab].
     
        [Sammet 1969, p. 506].
     
        [{Jargon File}]
     
        (1994-10-17)

flap
     
        1.  To unload a {DECtape} (so it goes flap,
        flap, flap).  Old-time {hackers} at {MIT} tell of the days
        when the disk was device 0 and {microtapes} were 1, 2,
        etc. and attempting to flap device 0 would instead start a
        motor banging inside a cabinet near the disk.
     
        The term is used, by extension, for unloading any magnetic
        tape.  See also {macrotape}.  Modern {cartridge tapes} no
        longer actually flap, but the usage has remained.
     
        The term could well be re-applied to {DEC}'s {TK50} cartridge
        tape drive, a spectacularly misengineered contraption which
        makes a loud flapping sound, almost like an old reel-type
        lawnmower, in one of its many tape-eating failure modes.
     
        2.  See {flapping router}.
     
        [{Jargon File}]
     
        (1997-06-17)