What is the 'Mankad' run out in cricket? What is the rule around it?

'Mankad' is a rare form of dismissal in which a bowler runs out the non-striker after the latter leaves the crease even before the ball is delivered. The dismissal is named after ex-India cricketer Vinoo Mankad, who first effected the dismissal in a Test against Australia in 1947. KXIP captain Ravichandran Ashwin 'mankaded' Rajasthan Royals opener Jos Buttler on Monday.