Isometric training is a special form of strength training through isometric contraction that tenses muscles but does not change their length.
Isometrically iso (= equal) and metric (= the measure) literally means "equal measure" and here means "equal length", "of unchanged length". Unlike dynamic (auxotonic) training, the muscle is not moved, but a pressure or train, built against a wall, a door frame or with a rope or towel and held for several seconds. Operated regularly, isometric training increases muscle strength in a very short time.
An example of isometric training is arm wrestling.
Source: Wikipedia