Karen Shaw was the name of the woman that John Crichton lost his virginity to. In truth, Karen Shaw was Chiana, having accidentally time traveled with the rest of Moya's crew to 1985 CE.
Chiana had given the young Crichton her real name, which he misheard as Karen, and then mistook her cry of excitement to be the surname "Shaw". He believed her to be wearing a Halloween costume.
Later, when Noranti Pralatong used one of her powders to make the young Crichton forget his encounter with his future crewmates, Chiana placed a suggestion in his mind that he not forget Karen Shaw.
Either Karen Shaw was, in fact, a real person who Crichton lost his virginity to, or the time travel incident was actually always a pre-destined part of the history of the Prime Reality and did not alter the course of events at all.
Source[]
Karen Shaw is derived from Farscape.