Definition

The technical execution of an exercise, including posture, movement path, and joint positioning. The thing everyone ignores until they get injured, then suddenly becomes an expert on.

Example Usage

Your form breaks down on the last few reps - maybe drop the weight a bit.

Origin

General athletic and exercise terminology used since at least the early 20th century.

Fun Fact

Perfect form is actually counterproductive for some strength goals - controlled 'cheating' and form breakdown under heavy loads triggers adaptation, which is why powerlifters don't look like textbook demonstrations.

Source: General fitness and strength training terminology