Source : Webster's Revised Unabridged Dictionary (1913)

Welterweight \Wel"ter*weight`\, n.
   1. (Horse Racing) A weight of 28 pounds (one of 40 pounds is
      called a {heavy welterweight}) sometimes imposed in
      addition to weight for age, chiefly in steeplechases and
      hurdle races.

   2. A boxer or wrestler whose weight is intermediate between
      that of a lightweight and that of a middleweight.

Source : WordNet®

welterweight
     n 1: a weight of 28 pounds; sometimes imposed as a handicap in a
          horse race (such as a steeple chase or hurdle race)
     2: an amateur boxer who weighs no more than 148 pounds
     3: a wrestler who weighs 154-172 pounds
     4: a professional boxer who weighs between 141 and 147 pounds