The Collaborative International Dictionary of English v.0.48:

Dewlap \Dew"lap`\, n. [Dew + lap to lick.]
   1. The pendulous skin under the neck of an ox, which laps or
      licks the dew in grazing.
      [1913 Webster]

   2. The flesh upon the human throat, especially when with age.
      [Burlesque]
      [1913 Webster]

            On her withered dewlap pour the ale.  --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dewlap
    n 1: a hanging fold of loose skin on an elderly person's neck