To have the upper hand means to be in a position of advantage or control in a situation. When you have the upper hand in a game of chess, you're winning and your opponent is scrambling to catch up. When one team has the upper hand in a soccer match, they're dominating play and seem likely to win.

You might gain the upper hand in a negotiation by having information the other person doesn't have, or in an argument by making a point that's hard to counter. A boxer gains the upper hand when she figures out her opponent's weakness. The phrase suggests temporary control that could shift: when someone gains the upper hand, they move from a weaker position to a stronger one, but they might lose it again if circumstances change.

People often talk about trying to gain, get, or keep the upper hand, which shows it's something you work to achieve and hold onto, not something permanent.