[Sancho]

Iron Maiden has two guitarists.
Both play leads. Both play rhythm for the better part of the gig.
I don't consider Janick Gers a guitarist, before someone asks.

Judas Priest has two guitarists.
Both play leads. Both play rhythm for the better part of the gig.

A rhythm guitarist is usually the guy who doesn't get to play leads.
Of course, there are exceptions. Like Rudolph Schenker.

A lead guitarist is the guy who gets to hog the spotlight. But inbetween leads, he plays rhythm. And can be damn good at it. John Sykes comes to mind. He's a far more inspiring rhythm guitarist than most dedicated rhythm guitarists...