Simplify the following text for a Grade 15 native English-speaking person.
Original: The Official Municipality Key , formerly also known as the Official Municipality Characteristic Number or Municipality Code Number , is a number sequence for the identification of politically independent municipalities or unincorporated areas .
Simplified: The Official Municipality Key , which used to be called the Official Municipality Characteristic Number or Municipality Code Number , is a group of numbers used to tell the difference between different municipalities and areas .