A more thorough explanation:

Qui tam is a legal term that comes from Latin. It means "who sues on behalf of the King as well as for himself." In a qui tam action, a person called a relator brings a lawsuit against a person or company on behalf of the government. The government is considered the plaintiff, not the relator. If the government wins the case, the relator who brought the lawsuit gets a share of the award.

For example, the federal False Claims Act allows qui tam actions against people or companies who have cheated the government. If the relator wins the case, they can get up to 30% of the government's award. In 2009, the Supreme Court heard a case called United States ex rel Eisenstein v. City of New York, which involved a qui tam action under the False Claims Act.

Another example of a qui tam action is a whistleblower lawsuit. Whistleblowers are people who report illegal or unethical behavior by their employer. If the government investigates and finds that the employer broke the law, the whistleblower may be able to bring a qui tam action and get a share of any money the government recovers.

Overall, qui tam actions are a way for private citizens to help the government catch people who are cheating or breaking the law. They can also be a way for whistleblowers to get compensation for speaking up about wrongdoing.