The gradual decrease in reactor fuel rod temperature caused by the removal of heat from the reactor coolant system after the reactor has been shutdown.

The time it takes for an item or special attack to pass before it can be used after initial use. 

The amount of time you have to feel depressed between using cool attacks.

The waiting time before a spell, item or ability can be used again.

The time you need to wait before being able to use a certain ability again.

The minimum amount of time that a champion must wait between consecutive casts of a spell. Cooldowns can be reduced by purchasing Cooldown Reduction