The Collaborative International Dictionary of English v.0.48:

moonwalk \moonwalk\ n.
   1. a kind of dance step in which the dancer seems to be
      sliding backward on the spot; as, Michael Jackson
      perfected the moonwalk in the 1980s.
      [WordNet 1.5]

   2. an exploratory walk by an astronaut on the surface of
      Earth's moon.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

moonwalk
    n 1: a kind of dance step in which the dancer seems to be
         sliding on the spot; "Michael Jackson perfected the
         moonwalk in the 1980s"
    2: an exploratory walk by an astronaut on the surface of the
       moon