Organizationally decentralized, logically centralized

Organizationally centralized are systems that are controlled by a single organization. Organizationally decentralized are systems that are not under control of any one entity.

Logically decentralized are systems that have multiple databases, where participants control their own database entirely. Excel is logically decentralized. Logically centralized are systems that appear as if they have a single global database (irrespective of how it's implemented).