Once judgment has been rendered against the defendant, there are a number of ways that the insurance company (assuming the defendant is insured) might later be made to pay the victorious plaintiff.
If the plaintiff wants to avoid the extra time and process required to eventually be paid by the insurance company, the action can be brought directly against the insurance company.
This name can also be given to any lawsuit that is brought as a kind of direct action activism.
One example can be a customer suing a company to repeal an action deemed an infringement on the rights of the customer as a citizen and thus a subject to federal or state law.
The largest direct-action lawsuit in history ($333 million) was the subject matter of the motion picture Erin Brockovich.