What component of a revolver holds the rounds and advances them after each shot?

The component of a revolver that holds the rounds and advances them after each shot is the cylinder. The cylinder is a rotating part of the revolver that contains multiple chambers, each designed to hold a single round of ammunition. When the revolver is fired, the cylinder rotates to align the next chamber with the barrel, allowing it to be fired in succession. This mechanism is crucial for the revolver's operation, as it enables multiple shots to be fired without the need for reloading after each shot, distinguishing it from other firearm types.

The other components, while vital to the revolver's functionality, do not serve this specific purpose. The slide is primarily found in semi-automatic pistols and is responsible for chambering the round and ejecting the spent cartridge. The trigger is the mechanism that initiates the firing process when pulled, and the barrel is the part through which the bullet travels when fired but does not hold the ammunition or advance it. Hence, the cylinder is the correct answer for holding and advancing the rounds in a revolver.