In baseball what is a sacrafice?

Official Baseball rule 10.09 (a) Score a sacrifice bunt when, before two are out, the batter advances one or more runners with a bunt and is put out at first base, or would have been put out except for a fielding error. (b) Score a sacrifice bunt when, before two are out, the fielders handle a bunted ball without error in an unsuccessful attempt to put out a preceding runner advancing one base.