The Collaborative International Dictionary of English v.0.48:
Appaloosa \Appaloosa\ n. 1. a hardy breed of horse developed in western North America and characteristically having a spotted rump. [WordNet 1.5]WordNet (r) 3.0 (2006):
Appaloosa n 1: a hardy breed of saddle horse developed in western North America and characteristically having a spotted rump