Production BOM contains the list of items needed to make an item. The items used as input are known as components while the outputed item coule be a finished good or a subassembly (to be used an component for to produce another item).
Single-level production BOM means all components used are purchased. Multi-level production BOM consist of one or more subassembly as the components. Navision can support up to 50 levels BOM.