See Kata

Kata

is a Japanese word describing detailed choreographed patterns of movements practised either solo or in pairs. The term form is used for the corresponding concept in non-Japanese martial arts in general....

 for "Form" as used in the context of martial arts.

Form is a specific way of performing a movement, often a strength training

Strength training

Strength training is the use of resistance to muscular contraction to build the strength, anaerobic endurance, and size of skeletal muscles. There are many different methods of strength training, the most common being the use of gravity or elastic/hydraulic forces to oppose muscle contraction...

 exercise, to avoid injury, prevent cheating and increase strength.

'Proper form'

Exercises or drills in sport have a recognized way of performing the movements that have two purposes:

Avoiding injury

By using proper or 'good' form, the risk of injury is lowered. A lack of proper form commonly results in injury or a lack of effect from the exercise being performed

Maximize benefit

Good form ensures that the movement only uses the main muscles, and avoids recruiting secondary muscles. As a muscle fatigues, the body attempts to compensate by recruiting other muscle groups and transferring force generation to non-fatigued units. This reduces the benefits in strength or size gain experienced by the muscles as they are not worked to failure.