What is the difference between a saber and an epee?

The blade of a Sabre is flat; in an épée, it is a v-shape; the guard of a Sabre is slightly rounded and extends round to the pommel, covering the knuckles; in épée, it is vaguely bell-shaped. In épée, hits can only be scored with the point of the weapon, whereas the edge can be used as well as the point in Sabre. In épée, if both fencers hit each other simultaneously, both score. In Sabre, the same system of priorities exists as in foil (if you don't know this system, sorry, but it's too complicated to explain in detail here). Finally, épée hits can be scored anywhere on the opponent's body, whereas Sabre hits on the hands and legs are invalid. This is not an exhaustive list, but it covers the main points.