Source : Webster's Revised Unabridged Dictionary (1913)

Spun \Spun\,
   imp. & p. p. of {Spin}.

   {Spun hay}, hay twisted into ropes for convenient carriage,
      as on a military expedition.

   {Spun silk}, a cheap article produced from floss, or
      short-fibered, broken, and waste silk, carded and spun, in
      distinction from the long filaments wound from the cocoon.
      It is often mixed with cotton.

   {Spun yarn} (Naut.), a line formed of two or more rope-yarns
      loosely twisted.

Source : WordNet®

spun yarn
     n : (nautical) small stuff consisting of a lightweight rope made
         of several rope yarns loosely wound together