The "three links" of trade, mail, and air and shipping services between mainland China and Taiwan; specifically 通商 tōng​shāng, 通邮 tōng​yóu, and 通航 tōng​háng

A pipe fitting or plug with three connection ports, such as a tee joint or three-way plug

The three basic utilities that must be provided to a construction site: water, electricity, and road access

Collective name for the three classic encyclopedic works of institutional history: 通典 tōng​diǎn, 通志 tōng​zhì, and 文献通考 wén​xiàn​tōng​kǎo