Long -
In simple terms.
1. Shroud - The large, thin walled tube that covers the barrel. On its own, rarely does much, but make the barrel look larger in diameter.
2. Moderator, Suppressor, Silencer, (and my favorite)...Muffler - The canister (of differing dimensions) that help quiet the report from the end of the barrel after the trigger is pulled. Can be a singular walled off tube, with a hole in the center for the pellet travel, that sits inside of the outer canister. Or, it can be made of seperate baffles, also inside of the outer canister.
These normally are attached to the end of the barrel OR the shroud (or an adapter), and are attached by 1/2" x 20 (unf), or M20 x 1.
3. Shroud-moderator - On SOME guns, the shroud has "baffles" inside of it. Daystate Renegade and Pulsar to name two. There are many more. It can also be a singular piece of material with, like above, can be walled off with a hole for the pellet to travel through. The Edgun Lelya, Lelya 2, Matador, and others, or. separate baffles, like some of the the Daystate shrouds.
Mike