PLU stands for Price Lookup Unit. It is mainly used as an alternate reference to stock.
Newsagencies
The PLU is one of the most important fields for newsagencies, as it is used for magazine and newspaper orders to customers (putaways and deliveries) and subagents.
They can be added by simply opening up a particular stock item in the Stock Screen, and typing in a PLU, then clicking Save.
A PLU should be entered on magazine parent items to prevent issues with incorrect arrival/sales data going to XchangeIT.
Non-Newsagents
PLU can be used with stock items in general, to easily find them from the Point of Sale screen.
You can add a PLU to a stock item by finding a particular stock item in the Stock screen, then typing in a PLU, then clicking Save.
Once assigned, you can open up the Point of Sale screen, and type in the PLU (in the white box for barcodes or searching), press Enter and your stock item should show up.