apostate: a mage who is not part of the Circle of Magi
Chantry of Andraste: the predominant religious group in Ferelden, based on Chant of Light, a series of teachings written by Andraste, the prophet of the Maker.
Circle of Magi: the dominant organization in Ferelden for the training of magic-users, under control of the Chantry.
darkspawn: Underground-dwelling hive-mind creatures in search of a master. When that master (the Archdemon) is found, the darkspawn swarm to the surface and kill all other beings they encounter. When this happens, it's referred to as a Blight. The swarm only ends when the Archdemon is defeated. Then the darkspawn return to the underground and begin the search anew.
Grey Wardens: an ancient organization of warriors of exceptional ability dedicated to fighting darkspawn.
maleficar: a mage who practices forbidden arts, including blood magic
Order of Templars: the military order of the Chantry that hunts apostates and maleficars and watches over the mages from the Circle of Magi. Templars have the ability to dispel magic and inhibit spellcasting. They're viewed by most people as holy warriors, keeping forbidden magic at bay.