Spell shields refer to one of several effects that have the capacity to negate enemy abilities.
Single ability
The following will block one enemy ability, with precedence given to the ability spell shield. If the ability is of an enhanced basic attack (e.g. 
Harsh Lesson, 
Power Fist) the spell shield will not block the damage of it, but only any additional effect it might have, like crowd control. In the case of Harsh Lesson, the spell shield breaks even if the attack doesn't have any crowd control effect with it.
Champion abilities
Items
Other
Morgana's Black Shield which instead of negating one ability, absorbs magic damage and makes the champion immune to crowd control.- Fiora's Riposte which blocks all incoming enemy crowd control effects, as well as non-turret damage.
- Olaf's Ragnarok
