Difference Between Client , Purchasing Org , Plant , Company code

What is the technical difference between Client , Purchasing Org , Plant , Company code?

Client : Unit within SAP system, self-contained, separate master data with independent set of tables. It represent corporate group.

Company Code : Smallest organisational unit of external account for which a complete, self-contained bookkeeping system can be replicated. eg, company within a corporate group.

Plant : An organisational unit within logistics, subdivides an enterprise from the viewpoint of production, procurement and materials planning.

Purchasing Org : Organisation within logistics which subdivides an enterprise according to purchasing requirements.

The procurement business process uses this organisational structure:

Client--->Company Code--->Plant--->Storage Location--->Purchasing Org/ Purchasing group