TLDR: read the whole thing and get educated

Real TLDR: A relay sends notes (tweets) from one user to the next. It literally "relays" your notes.

-----

Put simply, relays serve as hubs to push notes from one user to another.

When you post a note, your app sends that note to all the relays you're connected to. Each relay then sends that note to all the other users that are also connected to that relay.

A relay does exactly as the name suggests, it relays notes from one user to another.

Relays are usually denoted as wss://example.nostr.relay

Sort of like a https://www .website.com but instead of https:// it uses wss://

You can add as many relays as you want but the more you add the more battery power your app will consume.

Some relays are paid relays (you must pay to connect) and others are free. Typically paid relays will filter spam for you. Relays have the ability to filter the type of content they send out.

Hope that's helpful!