A case of concurrent jurisdiction arises where more than one court of different types come to a case falling in their jurisdiction. This often leads to a situation where parties involved would want the case to be heard in the court which seems advantageous to them.
Federal and state courts usually have concurrent jurisdiction over smaller, civil lawsuits. For example, an action which may lead to the declaration of a state law as unconstitutional. Other than that federal courts enjoy exclusive jurisdiction over many types of cases like those involving patents.