Repel was a spell acquired and used by Kain during the events of Blood Omen: Legacy of Kain.
Kain found this spell in an underground passage of one of Coorhagen's houses. When used, this spell created a magical shell around Kain, protecting him from all of the attacks of his enemies (excepting floor spikes) and reflecting back any projectile until the barrier wore off.
When Kain uses a control spell like Spirit Wrack or Control Mind over an enemy, he will automatically surround himself with a repel-like barrier, protecting his own body while manipulating his enemies.
This ability may be related to the similar 'barriers' used in later games; such as the repulsive blast used by Kain in the opening video ofSoul Reaver 2 against Raziel; or inLegacy of Kain: Defiance as a regular combat ability of Kain used to bring close and repel enemies with his telekinesis, and later by Raziel when he acquires Enhanced telekinesis after devouring the soul of his brother Turel. These barrier could may be of telekinetic or magical nature and they appear to be much shorter lived than repel.