The term originated during the Burning Times, when the Inquisition sweeped across the lands and put a fiery end to the open rule of the Cainites. It denotes more often than not vampire-hunters, but it's not applied to the Imbued.
Witch-Hunters can be trained by certain clerical organizations such as the Society of Leopold, secret societies like the Arcanum, or come from special government sections that focus on supernatural threats. Some are even criminals that have been confronted by the supernatural early in their life and have chosen to fight it on their own.
The vulgar argot for witch-hunter come in the form of the word Stalker.