It means that a person is legally entitled to obtain a divorce without having to show fault by the other person. Used to be you had to show that the other person did something wrong, like adultery, before you could just walk out on your marriage without having consequences imposed upon you by the court. No more.
But this isn't true everywhere in the USA, is it? Aren't there states where you can't get a no-fault divorce unless both parties want it, and the marriage is childless?