Underboob refers to the bottom of the boobs (wooow) winking at you from under the crop top. Nipslip is not included.
The term, underboob was probably created to the likeness of side boob, a term born in 1997.
Underboob was first mentioned in 1999 in a deodorant commercial, where a woman is complaining about how sweaty it can get there.
It gained prominence in 2015, when the Thai government made a statement how many dangers selfies with underboob impose on society… real shit.
In 2016, the internet answered to this statement with the underboob challenge, most widespread in Japan and China.
In this challenge, women were displaying their buxom talents by holding a pen with their mammaries.
Soon after though, the challenge was mocked by several users, by posting an “underboob challenge picture” with the pen being taped to them, or held by their hands.
In the following year, clothing companies started to tailor crop tops, so that the under cleavage is visible for the perceptive eyes… and all others, possibly.
Tattoos in this region of the body also gained prominence, with posts of women showing off their assets pouring out of Instagram around that time.
Several articles were published of this fashion trend, just like of sideboob a few years before it.