No fault insurance means that each party in an accident is covered, for medical, by their own insurance policy, regardless of who caused the accident. Many states require no fault policies by law.
The rationale behind no fault laws is to try to prevent needless litigation and random finger pointing and blame in an accident. It also leads to faster payments by insurers as there is no need for litigation, which holds payments.
Critics argue that this does not sufficiently punish unsafe drivers, however, since their insurance does not bear the entire responsibility in the accident.
Please remember, no fault only applies to medical coverage. Any property damage or other liability is borne by the responsible party.