Though its name is innocuous enough, Animation is the art of granting artificial (or false, depending on who you ask) life to that which is dead, and imbuing it with power. The spells Necromancers cast to raise the dead as their minions as well as grant them power belong in the Animation field. Regardless of how it is used, the gods view the creation of life as their territory, and Forsake those who tread here too heavily.
Animation is a thematic spellbook, borrowing spells that would otherwise fit into Blood Magic or Corruption if it involves meddling with the undead. Animation is used to create undead minions, manipulate the undead in various ways, and strike at the animating force behind other Necromancers' creations.
It is important to note that the undead creations of the Animation spellbook are always temporary, and often vanishingly so. Necromancers must invest the time and effort of creating a Risen -- a far more hands-on project than merely casting a spell -- if he wishes to have a long-term minion.