FAULT VS. NO FAULT: In some states, a person suing for divorce must prove that his/her spouse did something wrong (e.g., committed adultery). This is called "fault" divorce because one spouse is "at fault" or to blame. Other states offer "no fault" divorce.
In the case of "no fault" divorce, the person suing for divorce simply states his/her reason for wanting a divorce without accusing the other person of wrongdoing. Some "no fault" states require couples to be separated for a period of time before they can divorce.