A short manual work segment used to describe the sensory-motor activities or other basic elements of an operation. Developed by Frank and Lillian Gilbreth, therbligs form a basic language for methods description and, in modified form, for elemental motion time data. The original seventeen are: search, select, grasp, transport empty, transport loaded, hold, release load, position, preposition, inspect, assemble, disassemble, use, unavoidable delay, avoidable delay, plan, rest for overcoming fatigue. Syn: Gilbreth basic element, basic division of accomplishment, fundamental motion, basic motion, basic element. (Therblig spelled backwards is Gilbreth.)