The term 'Heat or Energy Unit' can be summarized by the crossword solution JOULE, which is a five-letter word. JOULE is a unit of energy or work in the International System of Units (SI). It is named after the English physicist James Prescott JOULE and is equal to the energy expended in applying a force of one newton through a distance of one meter. Joules are used to measure energy, work, heat, and mechanical power.