组(zǔ) - group, team; set (measure word); to form into a group in Mandarin

组 (zǔ) is a group in the organised sense: a working group, a class split into teams, a study group. It is smaller and more task-shaped than 团队 (tuán duì), which is a team as an ongoing unit, and it is the word teachers use when they divide a class.

It doubles as a measure word for things that come as a set, so 一组数字 is a set of figures and 一组照片 is a series of photographs. This is the sense you meet most often in reading, and it does not need a separate word in Mandarin the way English needs "set of".

As a verb it means to form or assemble, but almost always inside a compound rather than alone: 组成 (to make up), 组织 (to organise), 组合 (to combine). Leading roles get 组长, the group leader. Note the third tone, zǔ, which is easy to flatten next to a following fourth tone in 组织.