Historically, “cause of action” has had more than one meaning. Today, when lawyers in the United States refer to a “cause of action” they usually mean a legal category or legal theory on which someone bases a lawsuit. Remember, “action” means a lawsuit. Cause of action would mean the legal grounds for the lawsuit, such as breach of contract or tort.
For example, in the illustration below the pedestrian’s “cause of action” against the driver will be the tort of negligence because the driver carelessly injured the pedestrian while he was crossing the street.
In some cases a party might assert multiple causes of action for one injury. For example, a plaintiff might argue that he has a cause of action for breach of contract because the defendant broke a promise. In the alternative, the plaintiff might also claim to have a cause of action for fraud because the defendant lied when he made his promise.