The Collaborative International Dictionary
isometric exercise \i`so*met"ric ex"er*cise\, n. A system of exercise to strengthen specific muscles of the body by pushing parts of the body (such as the two hands) strongly against each other, or against a fixed object, so that the muscles are strongly stressed, but are stretched only a little. It is claimed to produce strength in the muscles thus exercised. Also called isometrics.
WordNet
n. muscle-building exercises (or a system of muscle-building exercises) involving muscular contractions against resistance without movement (the muscles contracts but the length of the muscle does not change) [syn: isometrics]
Wikipedia
Isometric exercise or isometrics are a type of strength training in which the joint angle and muscle length do not change during contraction (compared to concentric or eccentric contractions, called dynamic/isotonic movements). Isometrics are done in static positions, rather than being dynamic through a range of motion. Plank is one of the most popular isometric exercise, as it challenges all core muscles.
Usage examples of "isometric exercise".
After burning off excess physical energy with isometric exercise, he would allow himself a half hour of middle-density meditation.
She had been moving through the routine for five minutes, and it was superb isometric exercise for her.