A therblig is the name for the unit of time required for a worker to perform one of a set of fundamental motions while performing a manual operation or task. The set consists of 18 elements, each describing a standardized activity. These are listed below.

• Search
• Find
• Select
• Grasp
• Hold
• Position
• Assemble
• Use
• Disassemble
• Inspect
• Transport loaded
• Transport unloaded
• Pre-position for next operation
• Release load
• Unavoidable delayDefinition for: therblig

The fundamental motions of the hands of a worker.These operations are made up of 17 types of motion: search, select, grasp, reach, move, hold, release, position, pre-position, inspect, assemble, disassemble, use, unavoidable delay, avoidable delay, plan, and test to overcome fatigue.Frank Bunker Gilbreth defined these motions in his system of motion study.(Therblig is Gilbreth spelled backwards).

• Avoidable delay
• Plan
• Rest to overcome fatigue

The Therblig is used in the study of motion economy in the workplace. Each of the Therblig units for a process is timed, usually to the millisecond. These can then be compared to documented values for standard workplace tasks, and the results used for optimization of manual labor by eliminating unneeded movements.

The word Therblig is a reversal of the word Gilbreth, with 'th' treated as one letter. It was the creation of Frank Bunker Gilbreth and Lillian Moller Gilbreth, the American industrial psychologists who invented the field of time and motion study.