T-back
/ˈtiːbæk/noun
1- a high-cut undergarment or swimming costume having only a thin strip of material passing between the buttocks丁字形内裤（或泳裤）。
1.1
- a style of back on a bra or bikini top in which the shoulder straps meet a supporting lateral strap below the shoulder blades（胸罩或比基尼上装的）倒丁字形背带。