Used as a noun meaning something that is threefold, or as a prefix in compounds like トリプルアクセル (triple axel).
彼はフィギュアスケートでトリプルアクセルを跳んだ。
He landed a triple axel in figure skating.
このホテルの部屋はトリプルルームです。
This hotel room is a triple room.
She landed a triple during her routine.
The batter hit a triple with the bases loaded.