Thong underwear and swimwear is a style characterized by a thin strip of material along the center of the garment's rear designed to sit between the wearer's buttocks cheeks connecting the front or pouch to the waistband behind the wearer.

Thongs come in a variety of styles depending on the thickness, material, or type of this rear portion of fabric and are available for both men and women throughout the world.

Thongs are similar to g-strings, the main difference being that thongs have more material between the legs and back whereas a g-string has less, usually an actual "string" of material.

Retailer FreshPair defines thong as "An underwear style for both men and women with a thin fabric back that rests between the buttocks" whereas a g-string is "A panty with a very thin (string-like) band of fabric in the back."

Types of thongs include the traditional thong, the g-string, and v-string.