The term EXERCISE BYPRODUCT is composed of two words: EXERCISE and BYPRODUCT. The first word, EXERCISE, is a five-letter word that can be defined as physical activity that is done in order to maintain or improve health and fitness. The second word, BYPRODUCT, is a nine-letter word that can be defined as something produced as a result of a particular process or activity. In this case, the byproduct of EXERCISE is SWEAT. SWEAT is a salty liquid secreted by the SWEAT glands in the skin of mammals, which helps to regulate body temperature.