Real Dictionary

balance beam in American English
a long, narrow, horizontal wooden beam raised about 4 feet (1.2 m) above the floor, on which women gymnasts perform balancing routines consisting of jumps, tumbles, turns, running steps, etc.
noun: a narrow wooden rail about 16 ft. (5 m) long and 4 in. (10 cm) wide, set horizontally on upright posts about 4 ft. (1.2 m) from the floor, used for performing feats of balancing and demonstrating gymnastic ability