Absorption is a wide avoidance mechanic available to both NPCs and players. It is most commonly triggered by spells and items.
Absorb can be general or school-specific. Spells such as Power Word: Shield, Sacrifice, or Ice Barrier allow general absorption (Physical and all spell schools). Items such as Fire Protection Potions and spells such as Frost Ward allow absorption of a specific spell school.
Absorbing the effect of a spell does not make the player avoid the secondary effects of a spell such as snares, etc.