* centralized - a single funnel by which all traffic is managed, such as a web server
* federated - various disparate nodes comprising a centrally managed/governed network. This is blockchain and IPFS where the network is an application layer protocol. The more appropriate description is pseudo-decentralized or semi-autonomous. It is not centralized but it is also not fully decentralized.
* decentralized - disparate nodes communicating directly using agreed upon conventions. There is no centrally managed network. Think in terms of snail mail, IPv6, or phone numbers. This could be as simple as people using an agreed upon application to abstract away the transmission concerns but that application does not route traffic through a third party server.
The greatest misconception, or rather abuse of the term decentralized, I am seeing on HN is confusing it with a federated scheme. Federated schemes are not decentralized. Web3 is not decentralized. They are distributed.
In some cases the abuse of these terms is accidental, but it seems in many cases it is intentional. I suspect some large organizations, yes I am looking at you Facebook and Andreesen-Horowitz, are fearing functional obsolescence, either in their investments or their properties, in the near future and so are attempting to validate their existence by muddying the waters. By functional obsolescence I mean what would you need Facebook for if you can directly transmit media, or micropayments, between friends and family without some sinister third party destroying your privacy. The commercial web has become very hostile to its users, so pending a proper convenient end-user application, there is little incentive to continue using the web.