A more thorough explanation:

The abbreviation ex rel. stands for the Latin phrase ex relatione. This phrase is used in legal proceedings to indicate that the plaintiff is suing on behalf of someone else. The person on whose behalf the suit is brought is called the relator.

Many government lawsuits are brought as suits ex rel. For example, if an employee of a company discovers that the company is committing fraud against the government, they may file a lawsuit ex rel. The employee would be the relator, and the lawsuit would be brought on their behalf.

Another example of a lawsuit brought ex rel. is a case where a citizen discovers that a company is violating environmental regulations. The citizen could file a lawsuit ex rel. on behalf of the government, which is responsible for enforcing those regulations.

These examples illustrate how the phrase ex rel. is used to indicate that a lawsuit is being brought on behalf of someone else. In both cases, the relator is someone who has information about wrongdoing and is seeking to hold the wrongdoer accountable.