A capacitor (or cap) is an electronic element that stores the energy. Pretty much like a battery, can be used to power things. Well, there are actually substantial differences in the way caps charge or discharge. But let’s focus on the amount of energy a capacitor can hold.
Did I say “power the things”? Well, this is actually how they are commonly used. They are first charged by the supply voltage and discharge soon after to stabilize (or update, smooth) the voltage whenever it drops or fluctuates. Millions and millions of cycles during their lifetime. Far more any battery can withstand. You can find dozens of such circuits in any electronic device. And similar ones – but the idea is always the same: store some energy and give it back.