The Collaborative International Dictionary of English v.0.48:

offal \of"fal\, n. [Off + fall.]
   1. The rejected or waste parts of any process, especially the
      inedible parts of a butchered animal, such as the viscera.
      [1913 Webster +PJC]

   2. A dead body; carrion. --Shak.
      [1913 Webster]

   3. That which is thrown away as worthless or unfit for use;
      refuse; rubbish.
      [1913 Webster]

            The offals of other professions.      --South.
      [1913 Webster]

WordNet (r) 3.0 (2006):

offal
    n 1: viscera and trimmings of a butchered animal often
         considered inedible by humans

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "offal":
   bilge, bilgewater, bones, carrion, chaff, culm, deadwood, debris,
   dishwater, ditchwater, draff, dregs, dust, filings, garbage, gash,
   hogwash, husks, junk, leavings, lees, litter, offscourings, orts,
   parings, potsherds, rags, raspings, refuse, riffraff, rubbish,
   scourings, scrap iron, scraps, scum, scurf, sewage, sewerage,
   shards, shavings, slack, slag, slop, slops, slough, stubble,
   sweepings, swill, tares, trash, wastage, waste, waste matter,
   wastepaper, weeds