Serial number
A code unique to one unit, so it can be told apart from every other unit of the same product.
A lot covers many units; a serial number covers exactly one. Phones (by their IMEI), laptops, tools, appliances and bikes carry one, and it's what warranties, repairs and theft reports refer to.
Tracking by serial means recording each code as it comes in and naming which one leaves with each sale. In Binhop, an item tracked by serial asks for its serials when stock is added, scanned one after another, and when it's sold, and shows each unit's whole history.
