Therblig

Therbligs are 18 kinds of elemental motions, used in the study of motion economy in the workplace. A workplace task is analyzed by recording each of the therblig units for a process, with the results used for optimization of manual labour by eliminating unneeded movements.
The word "therblig" was the creation of Frank Bunker Gilbreth and Lillian Moller Gilbreth, American industrial psychologists who invented the field of time and motion study. It is a reversal of the name "Gilbreth", with 'th' transposed.
The basic motion elements.
A basic motion element is one of a set of fundamental motions required for a worker to perform a manual operation or task. The set consists of 18 elements, each describing a standardized activity.
Example usage.
Here is an example of how therbligs can be used to analyze motion:
History.
In an article published in 1915, Frank Gilbreth wrote of 16 elements: "The elements of a cycle of decisions and motions, either running partly or wholly concurrently with other elements in the same or other cycles, consist of the following, arranged in varying sequences: 1. Search, 2. Find, 3. Select, 4. Grasp, 5. Position, 6. Assemble, 7. Use, 8. Dissemble, or take apart, 9. Inspect, 10. Transport, loaded, 11. Pre-position for next operation, 12. Release load, 13. Transport, empty, 14. Wait (unavoidable delay), 15. Wait (avoidable delay), 16. Rest (for overcoming fatigue)." (Motion Study for the Crippled Soldier, in Journal of the American Society of Mechanical Engineers, December 1915, page 671.)