A revolver is so named because the bullets are in a cylinder which revolves to supply a new round to be fired after each shot. A pistol is usually supplied by a magazine which is in the grip.
Without trying to reach a technical distinction on the weapon's nomenclature and the way that the English language works, consider these general rules:
A pistol, revolver, semi automatic and a...
It's the round which makes the difference, not the pistol. A .45 automatic pistol is going to be more powerful than a .38 revolver, for example. There are revolvers chambered in cartridges such as...
A revolver4 is a pistol, however if you're talking about semi auto vs revolver, or mm vs gauge...
Semi auto allows you to fire more rapidly and can carry more ammo, however many feel that a revolver...