Source : Webster's Revised Unabridged Dictionary (1913)

Protrusion \Pro*tru"sion\, n.
   1. The act of protruding or thrusting forward, or beyond the
      usual limit.

   2. The state of being protruded, or thrust forward.

Source : WordNet®

protrusion
     n 1: something that bulges out or is protuberant or projects from
          a form [syn: {bulge}, {bump}, {hump}, {gibbosity}, {gibbousness},
           {jut}, {prominence}, {protuberance}, {extrusion}, {excrescence}]
     2: the act of projecting out from something [syn: {projection},
         {jut}, {jutting}]