The act of a womans or mans underwear or bathingsuit getting swallowed by their buttox. In worse situations it may be referred to as a starving bum. Usually this happens for larger ladies that wear too small of bathinsuits because they think its attractive to look at cottage cheese.
<duDe> OMG@! look at the hungry bum
<man> yea dude, her fucking ass swallowed her whole bathingsuit