Neathage, Bottom Breasts Cleavage Girl

When the lateral aspects of the breasts are uncovered, it is known as side cleavage, sidewinders or sideboob.
Underside
Exposure of the underside of the breast, such as below an extremely short crop top, is known as neathage (a blend of underneath and cleavage), Australian cleavage (because of the reference to Australia as down-under), bottom cleavage, reverse cleavage or underboob.