In vampire culture, their term for a vampire who has "created" another (turned a human into one in other words). "Maker" is the vampire equivalent of a parent, and often Makers take the vampires they created under their respective wing, mentoring them as mortal parents or teachers would a child. According to Patsy LaRue, the Maker of Merrill Young, the bond between a vampire and his/her Maker is one that should not be tampered with. But by the time of the Mansbridge Experiment, the Elders have evidentally decreed that this bond is not an unbreakable one, and that a vampire can leave his/her Maker if he/she wants to.
Patsy LaRue is the only Maker who appears on the series. Essie Rachimova's Maker was apparently her 'Uncle Dimitri', but we are not told who the Makers of the other vampire students at Mansbridge Academy are. Not all Makers seem to consider the bond between them and their "children" sacred, as Karl Todman's Maker apparently just 'turned' him and abandoned him (it's possible the turning was meant to be a killing).