The Collaborative International Dictionary of English v.0.48:

Pahoehoe \Pa*ho"e*ho`e\, n. (Min.)
   A name given in Hawaii (formerly the Sandwich Islands) to
   lava having a relatively smooth or billowing surface, in
   distinction from the rough-surfaced lava, called aa.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

pahoehoe
    n 1: freely flowing lava