A "Perfect" Round occurs only when the P1 or P2 defeats the other without losing any health. A "Perfect" Round does not occur when one "Rings Out" the other, as this is rather a one-hit K.O and did not result in fully defeating the foe. A Perfect Round will result in a change of the quote the player says. e.g. Rather than Nightmare saying, "Drown in the cesspool... Of darkness." He would say, "Gather before me, darkness of the abyss!"
"Excellent" rounds occur in Soul Calibur V. They occur when an opponent is able to defeat the other opponent at really low health. They are somehow the opposite of "Perfect" rounds.
In the Japanese version of the game, the round is referred to as "Great".