The Collaborative International Dictionary of English v.0.48:

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.
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            That the probation bear no hinge, nor loop
            To hang a doubt on.                   --Shak.
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   2. A small, narrow opening; a loophole.
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            And stop all sight-holes, every loop from whence
            The eye of Reason may pry in upon us. --Shak.
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   3. A curve of any kind in the form of a loop.
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   4. (Telegraphy) A wire forming part of a main circuit and
      returning to the point from which it starts.
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   5. (Acoustics) The portion of a vibrating string, air column,
      etc., between two nodes; -- called also ventral segment.
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   Loop knot, a single knot tied in a doubled cord, etc. so as
      to leave a loop beyond the knot. See Illust. of Knot.
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WordNet (r) 3.0 (2006):

loop knot
    n 1: any of various knots used to make a fixed loop in a rope