I am not the guy to solve semantic issues 😅

A relay is a server, but the name "relay" describes a certain set of behaviors that distinguish it from what we commonly call a server. A server is a computer running somewhere and a program running there that does something. We commonly think of *the* server in context of what we are doing; there is one server for your website, there is one server for your RSS feed, etc. A relay relays. It just takes messages and gives them to whoever requests them. You can send messages to many of them, people can request those messages from any of those. The distinguishing factor is that you're not tied to one as a publisher. They're just there, and you use them or you don't. You don't have to use a particular one, there isn't a particular one where your published information resides.

Essentially, yes. But these servers are simple to spin up and inexpensive to run if you’re not storing a metric ton of data. But if 1000’s of relays are all indexed by more than one indexer you get mighty powerful. All I can think of is Napster without that pesky centralization.

Okay, after more research, they're called relays because the relay messages between clients.