Sabre is a weapon which evolved from the cavalry sabre, and so has a few differences from the other two.
Sabre represents a fight between two cavalry officers on horseback.
The style of this fight means that, as well as scoring with the point, the edges of the sabre blade can be used to be used to score hits, in a cutting action.
Because of its origins on horseback, anything above the waist is counted as valid target area.
Sabre was the last of the three disciplines to be converted to electric scoring systems, and because of the difficulty in detecting a "correct" hit with the edge of the blade, electric sabre is still developing as technology improves.
Fast and Furious
Sabre is probably the fastest of the three modern fencing disciplines.
Top-level sabre fencers cover an enormous amount of distance very quickly, often moving from one end of the 14m piste to the other in two or three seconds. Even more surprising, considering they aren't allowed to cross their feet going forwards, so can't "run".