The school organized a sing-off where students competed to showcase their vocal talents.

sing-off 是由动词 sing（唱歌）和副词 off（离开、结束）组成的复合名词，字面意思是"歌唱对决"。这种构词方式模仿了"play-off"（季后赛）等体育术语，表示通过歌唱比赛来决出胜负的活动。