The thong typically resembles a bikini bottom, but at the back the material is reduced to a minimum.
Thongs are almost always designed to cover the genitals, anus, and perineum and leave part or most of the buttocks uncovered.
The back of the garment typically consists of a thin waistband and a thin strip of material, designed to be worn between the buttocks, that connects the middle of the waistband with the bottom front of the garment.
It is also used as a descriptive term in other types of garment, such as a bodysuit, bodystocking, leotard, or one-piece swimsuit, with the meaning "thong-backed".
No more visible panty lines: Wearing a thong underneath such dresses will help you avoid those.