Hands down, one of the finest aspects of a woman's anatomy that can be enjoyed in any public venue.
Underboob is achieved by wearing a very short halter top or cropped tank, also known as an underboob shirt, which exposes the bottom areas of a woman's breasts.
Much like the combination of low-rise jeans and a thong, the underboob shirt can only successfully be worn by select few women.
In an ideal situation, a hottie will wear an underboob shirt to accessorize her low-rise jeans/thong combination. When this happens, all men in the vicinity will regard her as "hot" or "a sexy bitch", while their wives/girlfriend may refer to her as "trashy" or "a slutty bitch", but that's okay. Everyone knows she's a sexy bitch and they all want to do her.