If a dominant position is any position where you have an overall advantage over your opponent, then an inferior position is any position where your opponent has an overall advantage over you. This may be because your opponent is on top of you and has a substantial gravity and body weight advantage, or may because you are stuck in an opponent's guard position where you can't effectively move or counter their attacks. Even though you should seek to be in dominant positions while grappling, you need to be skilled in inferior positions so that you don't let your opponent use dominant positions against you.