<P> The crena is another formal term for the cleft between the buttocks, and the medical term is posterior rugae . </P> <P> 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 . </P> <P> 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 . </P> <P> 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 from 2002 registers a design for trousers with a removable buttock cleavage - revealing portion . In the mid-2000s, Good Morning America reported on a rise of popularity of the buttock cleavage among celebrities . </P>

Where did the term plumbers crack come from