open-bust leotard
This is a type of leotard that became popular in the 1980s as part of the aerobics fashion craze at the time. As the name suggests, unlike most leotards, this garnment does not cover the chest and instead only features straps that come up from the waist to the shoulders, similar to a slingshot swimsuit with a leotard bottom. This type of leotard is also always sleeveless. It is intended to be worn with a shirt or two (often a crop top or bandeau) above and/or beneath it.
Examples include post #5600396 where one is worn with a bandeau, and post #5406426 (center) where it is worn with a sleeveless crop top.
This differs from breastless leotard which is a type of lingerie or erotic-wear intended to leave the breasts exposed, and is usually cut differently (sometimes omitting the straps altogether or combining them into a halterneck).