1. A serial number is a unique identifier assigned incrementally or sequentially to an item. Although it may be a characterstring that includes letters and other typographical symbols.
, 2. A serial number is a unique, identifying number or group of numbers and letters assigned to an individual piece of hardware, software or a pv module. Other things have serial numbers too, though, including banknotes and other similar documents.
, The idea behind serial numbers is to identify a specific item, much like how a fingerprint identifies a specific person.