The common use of mortal is as the antithesis to immortal. An immortal is someone who will, at least, never die of natural causes. At other times immortality includes invincibility to weapons and/or diseases. Mortals are normal humans, who are in mortal peril of all these things; age, disease and physical trauma.
In the Classic World of Darkness, however, the designation is commonly attributed to non-supernaturals, even when some supernatural groups are not immortal as such. The question is usually raised when discussing the imbued or mages, since they are closest to normal humans in a physical sense.
Just because the mortals have no innate powers, does not mean that they are helpless. Some mortals fight back and hunt the supernatural beings that walk among them. The capabilities of these mortal hunters (not to be mistaken with the Imbued) depend entirely upon their training, skills, and experience. While individual mortal hunters (or even small, loosely organized groups) are a minor threat to a supernatural community, there are large organizations that can be a major threat.
Two known governmental agencies that fight supernaturals are USA and Strike Force Zero in Japan. Ancient societies can be far more dangerous though, as they actually have knowledge about supernatural beings passed down through the generations. Two examples of these ancient societies are the Shih (in Demon Hunter X) and the Inquisition. The two primary reasons the ancient societies are so dangerous is: they know all about supernaturals AND they can be trained to use very powerful supernatural abilities and/or ancient weapons.in the
Many other types of "mortal hunters" exist in all the games. Information for these foes was often provided in the back of the main rulebook and in greater detail in "enemy" type sourcebooks. There was usually at least one enemy sourcebook for each game and the books also provided rules for players using mortal hunters in game.