When your Mana Shield, Frost Ward, Fire Ward, or Ice Barrier absorbs damage your spell damage is increased by X% of the amount absorbed for 10 sec.
Incanter's Absorption is a Magetalent in the Arcane tree. When you absorb damage, this talent turns a percentage of that damage into spell power, placing a buff on you.
It is possible to obtain both this talent and Ice Barrier at level 80, but not terribly advisable.
Patch changes
Patch 3.3.3 (2010-03-23): This talent now only grants additional spell power when damage is absorbed by Mana Shield, Frost Ward, Fire Ward, or Ice Barrier. The limit of 5% of the mage's health on the spell power buff has been removed.
Patch 3.0.8 (2009-01-20): Only adds spell power absorbed up to 5% of the mage's total health.
Patch 3.3.3 (2010-03-23): This talent now only grants additional spell power when damage is absorbed by Mana Shield, Frost Ward, Fire Ward, or Ice Barrier. The limit of 5% of the mage's health on the spell power buff has been removed. 
