Y-fronts
noun [ plural ] UK trademark uk/ˈwaɪ.frʌnts/ us/ˈwaɪ.frʌnts/
（前裆部呈倒Y形的）男式内裤
a brand name for a piece of underwear for men and boys, covering the area between the waist and the tops of the legs, with an opening at the front in the shape of an upside-down Y