The overhead squat is a real test of mobility and is one of the teaching progressions for the snatch.
Place the bar behind the neck with a snatch grip, from here perform a snatch push press driving the bar overhead securing it into a stable overhead position.
Keeping the elbow locked out and the chest up squat down, under control to the bottom of the squat and then drive back up keeping the bar stable throughout.
The overhead squat is a great strength builder of the upper body and trunk. It will help strengthen the receiving position in the snatch whilst working on mobility.
Generally speaking reps of 1-5 are most commonly used for strength. It can be used with light weights as a warm up to the snatch and on light days to keep the load down.