The other party; the opposing side or counterpart in a contract, negotiation, match, etc.
契約書に相手方の署名と押印をもらってください。
Please obtain the signature and seal of the other party on the contract.
交渉はまず相手方の要求をよく聞くことが重要だ。
In negotiations, it's important to first listen carefully to the other party's demands.
野球の試合で相手方が好投手を先発させてきた。
In the baseball game, the opposing team started with a good pitcher.