Centralized computers or networks is where all nodes communicate directly with a central authority.
An Ethernet switch is centralized in a hardware sense as all devices plug into a single switch. But from the perspective of the network this is not true.
Decentralized is were there is an ultimate authority, physically or just logically, and then layers of authority until the final node.
The IANA’s domain name system is decentralized in that there is a single root, multiple top level domains, followed by multiple second level domains, and continuing as necessary.
Distributed is where there may be multiple authorities with limited jurisdiction and potentially layered.
Countries are distributed in that they have no higher authority, but within each country are typically layers of authority.
It is worth noting that the logical and physical layout may be different. Consider Bitcoin as logically decentralized in that there is an ultimate reference, but physically distributed since that reference is not at one location.