A more thorough explanation:

Definition: A legal action brought by a private individual on behalf of the government, usually to recover money lost due to fraud or other illegal activities. This type of action is also known as a qui tam action.

Example: A whistleblower who works for a company that is defrauding the government can file a popular action to recover the money lost. If the case is successful, the whistleblower may receive a portion of the recovered funds as a reward.

Explanation: The example illustrates how a private individual can bring a popular action on behalf of the government to recover money lost due to fraud. The whistleblower in the example is acting as a representative of the government and is entitled to a portion of the recovered funds as a reward for their efforts.