Read on if you'd like to know...
In Brief...
Further information...
The reference is unique to you and can be anything you like which helps you identify that order. It might be something like "Dad's Birthday Present", or "Ink for printer".
This order reference is entirely optional, but is designed to help you distinguish one order from another. What you type in the order reference box is not seen by anyone, so please don't use it to communicate instructional information.
