A Judgement (ジャッジメント?) (as it's spelled in-game) is a system mechanic introduced in (and so far, exclusive to) the Street Fighter III series. It is an after-round decision that is made when a Double KO or Double Time-Up occurs on the final round of any given match.
Three judges appear holding signs that they slowly turn to reveal the winner of the match. The voting result is almost always 2:1, though straight 3:0s are possible, and the decision is made before the signs are turned. Judgements are made based on the grading system that is shown after matches. The player with the higher grade will be chosen as the winner.
At the end of this short video, a "judgment" is made to determine the winner.