合作 means 'cooperation' or 'to collaborate' and describes people or groups working together toward a shared goal. The character 合 (hé) means 'to join', 'to unite', or 'to fit together', while 作 (zuò) means 'to do' or 'to make'. Combined, 合作 literally conveys 'joint action' — emphasizing mutual effort rather than individual work. It’s commonly used in academic, professional, and community settings, such as team projects, business partnerships, or international agreements.

This word functions flexibly as both a noun ('cooperation') and a verb ('to collaborate'). As a verb, it usually appears with subjects and often takes an object (e.g., 合作完成项目) or is preceded by aspect particles like 在…中, 一起, or 与… (e.g., 与老师合作). It carries a formal, positive connotation and is rarely used for casual or spontaneous joint activities — those are more often expressed with 一起做… or 配合.