Archmage, archmagi, or archmagus is a title used to identify an especially powerful wizard. They are people who have, one way or another, gained the ability to influence the world around them in ways modern physics does not readily permit. This usually draws upon unusual energy sources, ranging from personal will-power to ambient arcane energy to naturally occurring ley-lines. In almost all cases they are a subset of wizards, magicians, druids, or other profession which uses said energy, albeit typically a highly disciplined and usually substantially more powerful and/or influential subset. A very good analogy (in most current fantasy uses) would be archmages are to wizards what a surgeon is to a doctor. Much more skilled in a certain area, although usually sacrificing some diversity in other areas.