triplet (one of a group of three siblings born at the same time to the same mother); treble (a team that wins three competitions in the same season); hat trick (three goals scored by one player in a game)
triptych; A three-part customs document allowing for the temporary importation of a motor vehicle into a foreign country without the need to pay customs duties.; The set of three fundamental and mandatory elements (tariff classification, origin, and customs value) that serve as the legal basis for classifying, valuing, and declaring any imported or exported goods.