Maleficar

Magic exists to serve man, and never to rule over him.
Foul and corrupt are they
Who have taken Her gift
And turned it against Her children.
They shall be named Maleficar, accursed ones.
They shall find no rest in this world
Or beyond.

A maleficar (plural maleficarum) is a mage who uses the forbidden arts including, but not solely restricted to, blood magic. Known maleficarum are slain on sight by templars.

Background

Apostates are not by definition maleficarum, but many are. Departing from the authority of the Circle of Magi usually leads a mage into exploring the forbidden, especially if they feel they need such power to stay alive. This is common enough that many templars will simply assume that any apostate is also a maleficar, or close enough to becoming one that it makes no difference.
Apostates who practice magical arts not well known among Circles are often referred to as maleficarum. This distinction is not exact and is usually born from the common ignorance and prejudice to associate all unique forms of magic with blood magic.