The Collaborative International Dictionary of English v.0.48:

piton \pi"ton\ (p[=e]"t[o^]n), n. (Mountain Climbing)
   A metal spike having a sharpened point on one end, and a hole
   through which a rope can be passed on the other; it is driven
   into the face of a rock cliff during climbing, and used as an
   anchor point for a rope.
   [PJC]

WordNet (r) 3.0 (2006):

piton
    n 1: a metal spike with a hole for a rope; mountaineers drive it
         into ice or rock to use as a hold