Buttock cleavage

Buttock cleavage is minor exposure of the buttocks and the intergluteal cleft between them, often because of low-rise pants. The crena is a formal term for the cleft between the buttocks.

History
When faced with indecency issues back in the 1930s, W. G. Cassidy explained in an essay titled "Private Parts: A judicial view" that exposure of a buttock cleavage may come under "other private parts" in Australian law, though indecency generally involves exposure of 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.

Jeffreys (2005) identified British designer Alexander McQueen as the originator of buttock cleavage-revealing jeans, known as the "bumster"; similarly, a 2002 U.S. Patent 6473908 registers a trousers design with a removable buttock-covering part for revealing cleavage. In the mid-2000s, Good Morning America reported on a rise of popularity of the buttock cleavage among celebrities. In an interview conducted in late 2002, pop singer Avril Lavigne said: "My buttcrack showing is like my trademark."

In 2010s, media reported rise in popularity among females of ultra-short miniskirts and shorts, which publicly exposed "underbuns" (i.e. lower part of buttocks, also referred as underbutts or "reverse buttock cleavage"), due to endorsement by celebrities such as Lady Gaga. Paparazzi also photographed Jessica Alba's tramp stamp bow tattoo, located just above her buttcrack cleavage.

Lexicon
The terms plumber butt or plumber's crack (Canadian, Australian, and American English) and builder's bum (British English) refer to the exposure of the 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 work in these professions frequently involves bending over in locations where bystanders are observing from the rear. In the Netherlands the term bouwvakkersdecolleté and in Germany Maurerdekolleté and in Poland dekolt hydraulika is used, which can be translated as "builder's/mason's/plumber's cleavage". In France, it is usually referred to as le sourire du plombier, which literally translates to "the plumber's smile".