A String Bikini refers to a bikini swimsuit worn by women that is scantier and more revealing than the traditional bikinis. It gets its name from the string characteristics of its design. Rather than featuring a full single piece bottom, the string bikini consists of two triangular shaped pieces connected at the groin but not at the sides, where a thin "string" wraps around the waist connecting the two parts. String bikini tops are similar and are tied in place by the attached "string" pieces. String pieces can either be continuous or tied. The cult favorite Humanoids From The Deep (1980) featured a string bikini worn by a festival mascot.

A String Bikini is also a type of undergarment worn by both men and women. It is similar to but more revealing than a bikini. Women's string bikini underwear normally resembles the bottom of the string bikini bathing suit. Men's string bikini underwear consists of a front and rear section joined at the crotch but not at the sides. The tops of each piece join with either an elastic waistband similar to that found on briefs or to a thin piece of material or "string," leaving the sides exposed except for the string or waistband.