The Collaborative International Dictionary of English v.0.48:

fragmentation grenade \fragmentation grenade\ n. (Mil.)
   A type of hand grenade designed to burst into multiple
   fragments upon detonation of the explosive charge; the
   fragments fly away at high velocity, killing or wounding
   persons nearby. Contrasted to concussion grenade. The
   common type of fragmentation grenade used by the American
   military was sometimes jocosely referred to as a pineapple
   from its reticulated surface appearance, resembling that of
   the fruit.
   [PJC]