What does Preferred Vendor stand for?

Preferred vendors are those vendors that you have designated as your vendors of choice for reordering items when they go low on stock.

You can set the preferred vendor in its respective field for an item by editing it or when you add an item to an item group using the Add item button, you can find it in the new item page.

When an item goes below its reordered point, if you have set up a preferred vendor for it, then you can reorder that item from the vendor contact page itself.