These are inventory and non-inventory items you create in Maintain Items and Maintain Non-Inventory Items. The IDs are used primarily to translate your internal item identifiers to the vendor item identifiers when working with purchase orders.

I hadn't thought about looking into the inventory module.  Thank you so much for this information.

You can also reference What's This? help from the right-click context menu for the control, online help from the form or the abbreviated manual for the module.