balance beam

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A horizontal raised beam with a width of 10 centimeters (4 inches) and a length of 5 meters (16 feet) that is used in gymnastic competition for balancing exercises.
• noun A competitive gymnastics event in which various balancing feats are performed on this beam.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun gymnastics A narrow wooden rail used in gymnastics.
• noun The horizontal member of any balance (scale,) usually carrying pans at each end, supported at its center by a fulcrum.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a gymnastic apparatus used by women gymnasts