A serial number (also manufacturer’s serial number or MSN) is a unique code assigned for identification of a single unit. Although usually called a number, it may include letters, though ending with digits. Typically serial numbers of a production run are incremented by one, or another fixed difference, from one unit to the next. Units may be marked with several alphanumeric codes, but only one of these will be a serial number; others are sometimes called nominal numbers, and may identify the part, specify installed options, and so on.
