The term "Conversion Day" appears in a number of works of fan fiction based on the Forever Knight television series. It refers to the anniversary of the day on which a vampire was brought across: a "conversion day" is to a vampire what a birthday is to a mortal. Indeed, vampires usually celebrate their Conversion Day instead of (rather than in addition to) the anniversary of their mortal birth.
It should be noted that Conversion Days are never mentioned in any of the actual episodes of Forever Knight. Although the concept has been employed by number of fans, it appears only in fan fiction. As such, Conversion Days should be considered an aspect of Forever Knight fanon.
A Conversion Day story is usually short, comprising events leading up to the celebration. Typically, the plot either involves the problem of selecting an appropriate gift, or uncertainty about the nature of the present that will be received.