Well the coils themselves don't have gaskets or seals around them, so I can only assume it means the rubber gasket that's on the plastic cover. (The cover that has the black and aluminium stripe effect on it). This is nothing more than a way of keeping muck and grime out of the spark plug area, but unless the seal tears or rips when you pull the cover off I wouldn't bother replacing it.
Technically to be 100% correct you would, but when I did my plugs a while ago I certainly didn't bother.
Technically to be 100% correct you would, but when I did my plugs a while ago I certainly didn't bother.