(jl, joul) noun. Abbr. j, J, joule 1. The International System unit of electrical, mechanical, and thermal energy. 2. a. A unit of electrical energy equal to the work done when a current of 1 ampere is passed through a resistance of 1 ohm for 1 second. b. A unit of energy equal to the work done when a force of 1 newton acts through a distance of 1 meter. [After James Prescott Joule.].