Your counterpart is the person — or the thing — that does the same job, or has the same place, as you, but somewhere else. The mayor's counterpart in another city is that city's mayor. A left glove's counterpart is the right one.

Your counterpart你的counterpart（對口） is the person — or the thing就是那個人——或那樣東西 — that does the same job, or has the same place, as you, but somewhere else跟你做同樣的工作、或處在同樣的位置，只是在別的地方。The mayor's counterpart in another city某個市長在另一座城市的counterpart就是那座城市的市長。A left glove's counterpart is the right one左手手套的counterpart就是右手那隻。

News and office English use it all the time for people: 'she met her counterpart in Tokyo'. It sounds a little formal, but it is not fancy.

News and office English新聞和辦公室英文 use it all the time for people很常用這個字指人: 'she met her counterpart in Tokyo'像'she met her counterpart in Tokyo'（她在東京跟她的對口見了面）。It它 sounds a little formal聽起來有點正式, but it is not fancy但並不浮誇。

Though actually the oldest use was drier: a counterpart was the matching copy of a legal paper, the other half of the same deal. That 'matching copy' feeling is still inside the word.

Though actually不過其實 the oldest use was drier最早的用法比較乾巴巴: a counterpart was the matching copy of a legal paper counterpart指的是一份法律文件對應的副本, the other half of the same deal也就是同一筆交易的另一半。That 'matching copy' feeling這種「對應副本」的感覺 is still inside the word現在還留在這個字裡面。

People sometimes use it as if it only meant 'the other person in the room', with no shared job at all. That is looser than the word wants.

People sometimes use it as if it only meant 'the other person in the room'人們有時候用起來，好像它只是指「房間裡的另一個人」, with no shared job at all完全不需要有共同的職務。That那樣 than the word wants比這個字原本的意思 is looser更鬆散。