Wiktionary
n. (''time and motion study'') Any of a set of fundamental motions required for a worker to perform a manual operation.
Wikipedia
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 labor 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.
Usage examples of "therblig".
Dad made a motion study, he broke down each operation into a Therblig, and then tried to reduce the time taken to perform each Therblig.
And he painted seventeen mysterious-looking symbols, representing each of the Therbligs, on a wall near the front door.
Dad believed, always makes the best use of his Therbligs because he is too indolent to waste motions.
Morse code, and planets, and even Therbligs, painted all over the walls of their house, either.