A G-string is a garment consisting of a narrow piece of material that covers the genitals, a string-like piece that passes between the buttocks, and a very thin waistband around the hips. There are designs for both women and men. Men's G-strings are similar to women's but have a front pouch that covers the genitals. G-strings are typically worn as underwear or swimwear or as part of the costume of an exotic dancer.

G-strings are usually made of fabric, lace, leather, or satin. They may serve as a bikini bottoms or they may be worn alone as monokinis or topless swimsuits. G-strings are also be worn by go-go dancers. As underwear, G-strings may be worn in preference to panties to avoid the creation of a visible panty line, or to briefs in order to enhance sex appeal.

The two terms G-string and thong are sometimes used interchangeably; however, technically they refer to different pieces of clothing. G-strings have a thinner back strip than thongs, and usually a thinner waistband. These connectors are often made of string rather than a strip of fabric.