A dominant position is any position where you have an overall advantage over your opponent, considering opportunities to pin the opponent's movement as well as opportunities to attack and submit. This is the flip-side of an inferior position, where your opponent has a dominant position over you, but you are trying to achieve the most effective defense or countering position within that. Dominant positions tend to put you on top of your opponent, where gravity and body weight can be more easily brought to bear, especially to isolate the limbs of your opponent in preparation for a submission.