The bulgarian split squat is a variation of lunges. If you haven’t looked at the lunge article yet I suggest you take a look at it. A bulgarian split squat will allow greater range of motion of the leg muscles. A greater range of motion translates to activation of more muscles and increased muscle strength over time.
To perform a bulgarian split squat, find a bench that is anywhere between 6 and 18 inches high. Stand with your back to the bench and place one of your feet on it (extended behind you). Once in position, use your other leg to squat down almost to the point where your knee of the leg on the bench touches the ground. Push back up and repeat.
The bulgarian split squat can also be performed with dumbbells or a barbell. This will help increase the intensity of the exercise if it gets too easy. You can also use a platform for one of your feet to make the exercise more intense (in video).
Bulgarian Split Squat Video