Saber is the American spelling of sabre. It is the same word: a sword with a curved blade, the kind horse soldiers used to carry. In sport fencing it is also one of the three weapons. British English usually writes sabre; American English usually writes saber. You will also see the American spelling in saber-toothed, for the big cat with long teeth. Though actually, some US fencing groups still write sabre, so the letters are not a perfect test of where a person is from — but in American school spelling, saber is the expected form.