A more thorough explanation:

The first-filed rule is a principle in civil procedure that states when two lawsuits are brought by the same parties regarding the same issues in two courts of proper jurisdiction, the court that first acquires jurisdiction usually retains the suit, to the exclusion of the other court. This means that the court with the second-filed suit typically stays proceedings or abstains.

However, there is an exception to this rule if the first-filed suit is brought merely in anticipation of the true plaintiff's suit and amounts to an improper attempt at forum-shopping. In this case, the second court may proceed with the case.

For example, if a person files a lawsuit in a state court and then files the same lawsuit in a federal court, the federal court will likely stay proceedings or abstain if the state court acquired jurisdiction first. This is because the first-filed rule gives priority to the court that first acquired jurisdiction over the case.

Another example is if a company files a lawsuit against a former employee in one state and the former employee files a similar lawsuit against the company in another state. If the company's lawsuit was filed first and the former employee's lawsuit was filed in anticipation of the company's lawsuit, the court may apply the first-filed rule and allow the company's lawsuit to proceed while staying or abstaining from the former employee's lawsuit.