Buttock cleavage is minor exposure of the buttocks and the intergluteal cleft between them, often because of low-slung or loose trousers. The crena is another formal term for the cleft between the buttocks.
When faced with indecency issues back in the 1930s, W.G. Cassidy explained in an essay titled Private Parts: A Judicial View that it may come under "other private parts" in Australian Law, though indecency generally covers the genital area.
In the early 2000s it became fashionable for young women and men to expose their buttocks this way, often in tandem with low rise jeans. The Cincinnati Enquirer called it the "new cleavage", and expressed views that "It's virtually impossible to find jeans to cover your hipbone". In August 2001, The Sun celebrated a "bum cleavage week" claiming that "bums are the new tits". In reaction to this trend, Saturday Night Live aired a parody advertisement in their April 16, 2006 episode for a product called Neutrogena Coin Slot Cream, in which host Lindsay Lohan appeared.
British designer Alexander McQueen was particularly mentioned as the originator of buttock cleavage-revealing jeans, known as the "bumster", in cultural critique Sheila Jeffreys' Beauty and Misogyny: Harmful Cultural Practices in the West. United States Patent 6473908 registers a design for buttock cleavage-revealing trouser designs. In the mid-2000s, Good Morning America reported on a rise of popularity of the buttock cleavage among celebrities.
The terms plumber butt (Canadian, Australian and American English) and builder's bum (British English) refer to the exposure of male buttock cleavage, especially on occasions of careless bending over. The expression "builder's bum" was first recorded in 1988. The terms are based on the popular impression that these professions are particularly prone to this kind of mishap.
In the Netherlands the term bouwvakkersdecolleté and in Germany Maurerdekolleté is used, which can be translated as "builder's/masoner's cleavage".
See also 
- Southerly: The Magazine of the Australian English Association, Sydney, volume 34, page 318, Australian English Association, 1939
- Brown, Janelle. "Here come the buns", Salon.com, URL accessed March 12, 2006.
- Jennifer D'Angelo, "Cleavage Fashion Flips Upside Down," FOXNews.com, December 5, 2001, URL accessed 12 March 2006.
- Daugherty, Gina. "Thong spotting gets easier", The Cincinnati Enquirer, May 29, 2003.
- Davies, Anna. "Bum deal: Suddenly, women's bottoms are everywhere. It might seem like jolly, harmless fun, but actually there's nothing innocent about it", The Guardian, August 27, 2001. Accessed February 19, 2008. "Last week was bum cleavage week at the Sun."
- "Saturday Night Live Skit - Neutrogena Coin Slot Cream". Youtube.com. Retrieved 2012-08-01.[unreliable source?]
- Sheila Jeffreys, Beauty and Misogyny: Harmful Cultural Practices in the West, page 98, Routledge, 2005, ISBN 0-415-35183-9
- Garment having a buttocks cleavage revealing feature, Patent Storm
- "Celebrities Are Showing Off Butt Cleavage", Good Morning America, July 25. Accessed February 19, 2008.
- "Brewer's Dictionary of Modern Phrase & Fable", by John Ayto, Ian Crofton (2006) ISBN 0-304-36809-1, p.121