Source : Webster's Revised Unabridged Dictionary (1913)

Loop \Loop\, n. [Cf. Ir. & Gael. lub loop, noose, fold, thong,
   bend, lub to bend, incline.]
   1. A fold or doubling of a thread, cord, rope, etc., through
      which another thread, cord, etc., can be passed, or which
      a hook can be hooked into; an eye, as of metal; a staple;
      a noose; a bight.

            That the probation bear no hinge, nor loop To hang a
            doubt on.                             --Shak.

   2. A small, narrow opening; a loophole.

            And stop all sight-holes, every loop from whence The
            eye of Reason may pry in upon us.     --Shak.

   3. A curve of any kind in the form of a loop.

   4. (Telegraphy) A wire forming part of a main circuit and
      returning to the point from which it starts.

   5. (Acoustics) The portion of a vibrating string, air column,
      etc., between two nodes; -- called also {ventral segment}.

   {Loop knot}, a single knot tied in a doubled cord, etc. so as
      to leave a loop beyond the knot. See Illust. of {Knot}.

Source : WordNet®

loop knot
     n : any of various knots used to make a fixed loop in a rope