noun
trio; group of three; threesome
Refers to a group or set of three people, often with a sense of them acting together. Can be neutral or carry a slightly informal, sometimes conspiratorial nuance depending on context.
あの三人組はいつも一緒にいる。
That trio is always together.
銀行強盗は三人組だった。
The bank robbers were a gang of three.
Compound of 三人 (three people) and 組 (group, set).