A squat on a Bosu ball is a type of exercise that combines the movements of a squat with the added challenge of unstable surface training. The Bosu ball is a fitness training tool that is shaped like a half-dome, with a flat platform on one side and an inflatable dome on the other. 

To perform a squat on a Bosu ball, start by standing on the flat platform of the ball with your feet shoulder-width apart and your arms at your sides. Lower your body down into a squat position, keeping your weight in your heels and your chest up. Push back up to the starting position, and repeat for the desired number of repetitions. This exercise can be done with or without added weight, such as dumbbells or weighted vest to increase the difficulty. The instability of the Bosu ball adds an extra challenge to the exercise and can help improve balance and stability.