Assembly BOMs specify which components or resources are required to assemble the item that the assembly BOM represents. Assembly BOMs usually contain items but can also contain one or more resources that perform the assembly work.
Assembly BOMs can be multilevel, which means that a component on the assembly BOM can be an assembly item itself.
Multilevel assembly BOMs can have special requirements in certain cases, such as availability, planning, and standard cost calculation.
Usually when you enter the assembly item on an assembly order header, the assembly BOM components are automatically filled into the assembly order lines and are then ready to be consumed in the assembly process (called in IFS blow through items).