Prestige Class is a secondary class of a character, attained when meeting some prerequisites.
Dashing Swordsman chosen by Elan, is a Prestige Class. We have also seen the Shadowdancer, another prestige class and Tsukiko's Mystic Theurge. Kubota strongly implies in #595 that he has levels in a prestige class that allows him to fool magical lie detection.
In #209, Elan references the Master Samurai and Mean Old Cranky-Pants prestige classes.