Use this field in the Purchasing and Receiving window when you are ordering by the unit in which the item is stocked. For example, items like paint, cleaners, and tools are stocked by the each, so you would put the order quantity for these items in this field. For example, if you wanted to order ten cans of paint, you'd enter 10 in this field.
In contrast, items like rope, chain, and wire are typically stocked by the foot, but purchased by the roll. To order these types of items by the foot, you'd enter the number of feet in a roll (for example, if there are 250 feet in a roll, you'd enter 250 in this field). However, an easier way to order these types of items would be to leave this field blank, and instead enter the number of rolls you want to order in the "Order Qty [Pur]" field.