In the Mortal Kombat series, a Flawless Victory is a feat achieved by winning a round without the player incurring any damage, including chip damage from blocking, over the course of a round.
Double Flawless
A Double Flawless is winning the entire match without incurring damage;including block damage, over the course of two rounds. The phrase is only used in the first and second games; from Mortal Kombat 3 onward, every no-damage victory is a Flawless Victory, whether or not it was preceded by another in the previous round.
Other media
The phrase Flawless Victory has, over time, become part of the popular culture vernacular. Persons will often refer to an exceptional accomplishment as a "Flawless Victory" so as to accentuate the superior nature of the feat, all the while paying homage to Mortal Kombat. The phrase has also been observed in contemporary film and television.