Focus is a buff that is used only by The Defect. Each stack of Focus increases the Passive and Evoke effects of Channeled Orbs by 1 (except for Plasma).
You can get Focus by casting the Powers Defragment (1 or 2 if upgraded) or Biased Cognition (3 or 4 if upgraded).
Biased Cognition also causes a Focus loss per turn, just like Wraith Form’s Dexterity lost per turn.