Here is Gustaf's definition of modular supply chain:
The lowest level is that you deliver one product from one business unit (or division), this is the Product supply chain.
The second level is that you deliver two or more products from two or more business units (or divisions). This could also be merged with products coming from local suppliers that are to heavy/bulky to transport between countries or regions. This is the System supply chain. To achieve this you take the Product supply chain and add some modules, e.g., processes, like coordination, local purchasing.
The third level is that you deliver a complete solution of products and services. This is the Solution supply chain which is the System supply cahin plus some modules, e.g., configuration, installation and could also include operation and maintenance.
You can also break up the simple Product Supply Chain in modules like warehousing, manufacturing, planning, purchasing etc and define what is the best way to execute the modules, e.g., outsourced, inhouse, partnership, common function shared bu different business units (or divisions).