Our band is going to perform a Welsh polka called "Moel yr Wyddfa" for the upcoming St David's picnic. (Forgive me if Wyddfa is spelled wrong - I don't have the actual music handy.) We know that Wyddfa is Mount Snowdon, but what does "Moel" mean?

Second question: we may do Llongau Caernarfon. Can anybody tell me in a few words what this air is about?