Rounds are what we call coins I guess, particularly if they don’t have a denomination on them. A shield I would say involves a gold sovereign which has St George & the dragon on one side normally but the earlier version had a shield.
Thanks for your reply STC - It doesn't seem to have St-George in all shields I see. I find it hard to find a common ground. I know rounds have no official value as a denomination compared to a round, but I can't wrapped my head around the concept of shields a presented on the vendor's pages. Maybe it's different in North America?