Definition and background:
A percussion instrument consisting of a set of metal bars which are sounded by being struck with a hammer. Each bar produces a specific tone. The bars are arranged in the same manner as a piano keyboard, and thus the orchestra bells are fully chromatic. The range is from g to c'' and sounds two octaves higher than written. Also see bell lyre, glockenspiel.
Bells consisting of tuned metal bars mounted on a rectangular frame and played with a mallet.
For more information on the music term "Orchestra bells" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary