I've started categorizing internet technologies/services into 3 categories based on how their infrastructure is architected.
Centralized: Basically every big service you know. The users of a service talk to one server or a network of servers all controlled by one person/organization. You're left up to their whims.
Distributed: There are still clients and servers, but the servers all speak a common language (known as a protocol) and can be operated by anyone. Some protocols have varying degrees of trust, with the Fediverse placing the trust of someone's data and identity in a single server operator and Nostr using trustless cryptographic identity and distributed data storage.
Peer to Peer: There are no servers. Users of the service directly communicate with each other, with few to no middlemen (BitTorrent trackers, STUN/TURN servers, etc).
