Wiktionary
n. (context euphemistic English) An accidental instance of indecent exposure caused by a fault in someone's clothing (especially that of a performer) or by an error made while changing this costume.
Wikipedia
A wardrobe malfunction is accidental exposure of intimate parts. It is different from indecent exposure or flashing, as the latter ones imply a deliberate exposure. There has been a long history of such incidents, though the term itself was coined in the mid-2000s and has become one of the most common fashion faux pas. Justin Timberlake first used the term referring to the Super Bowl XXXVIII halftime show controversy, issuing a scripted apology at the 2004 Grammy Awards. The phrase "wardrobe malfunction" has since been used by the media to refer to the incident and has entered pop culture.