How does 'serialisation' differ from 'unique identification' in the GS1 System?

Serialisation is the process or action of identifying something in a serial format, for “unique identification" it is the process of generating and applying codes or serial numbers that can be used to uniquely identify each individual instance of a given entity.  The "serial number" (which can be numeric or alphanumeric in form) is assigned to an individual instance of an entity for its lifetime, they can be sequentially or randomly generated and can be represented in human readable form (e.g. alpha-numeric text) and/or machine readable form (e.g. encoded with a GS1 barcode or RFID EPC tag).

An individual trade item may be identified uniquely with the combination of a Global Trade Item Number (or “GTIN” for the base product identification) and serial number (for the unique instance of that base product). Serialisation makes it possible to trace individual products as they move through the supply chain.

The following GS1 Identification Keys  have serialisation as an optional element:

There are also GS1 Keys that identify a specific instance: