Wardrobe malfunction is a euphemism used to describe the accidental exposure of an intimate part or parts of the body due to a defect in an article or articles of clothing.
read more on wikipedia
wardrobe malfunction n. A problem with a part of one's clothing.
Janet Jackson: Performing at the 38th Super Bowl Halftime Show, Timberlake pulled off a part of Jackson's costume, revealing her right breast.
Tara Reid: Arriving for P. Diddy's birthday party in New York, the strap of her dress slipped off her shoulder, exposing her left breast.
Keira Knightley: The British beauty had a slight dress slip at premiere of her new movie "Pride & Prejudice". The dress slipped down just enough to show off her left nipple.
Lindsay Lohan: The actress-singer has, at a Hollywood Fashion Show, accidentally revealed a little too much of her breast.