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.
Generally, when a women wears a short cut top/pulls up their top to cover all but a portion of the bottom of the breast. Nipple can be shown, but often it is also covered.
Other ways to achieve underboob are: Handbra (covering the breast in the same way a short cut top would), or viewing from a low angle so that the point of view is looking up at the woman's breasts.
Any short shirt, such as a halter top, cropped tank or baby tee, that rides so high on a woman's chest as to expose not just the midriff, but also the bottom area of a woman's bust.
The pools of sweat collected under large breasts. Usually under larger women's voluptuous bosoms. known to cause interesting sweat designs in t-shirts and can cause a number of problems.