What does chest to torso mean in BJJ?

Getting your chest onto your opponent's torso is required for nearly all dominant positions. You are either looking to get chest to back (for back control) or chest to chest (for mount, side control, north south). The sooner you get chest to torso, the better. Many takedowns and passes involve getting chest to chest or chest to back. It is a very controlling way to pass and offers less risk of scrambles.