The cooldown of an ability is a measure of how many seconds it takes to become ready again after it has been used.
Useful info below
Evidence of cooldownEdit
When an ability is used, the corresponding thumbnail in the ability bars becomes fully greyed out. It regenerates over time, turning back to whatever color it was before from the edge inwards.
Attempting to activate the ability will cause a red progress bar to be displayed at the top of the screen which shows how close you are to meeting the necessary criterion (often this is cooldown)
If there is any cooldown reduction active, the bar will NOT be moving any faster. Instead, with a 50% cooldown reduction, the bar will only grey out halfway, and regenerate from there.
Cooldown can be reduced through several things. For example, ability cooldowns are sometimes reduced flatly by a piece of equipment from the same node, such as the Accelatron or the Short-Cycle chamber.
The Ace drive offers cooldown reduction according to how many enemies you kill without dying.
Other abilities, like the maneuvering Battery, depend on a certain criterion to be met before the cooldown reduction becomes active, in this case the rocket needs to hit a target.
Some abilities can finish cooldowns instantly.