Nostr is a network protocol for building decentralized social networks. It is built on the secp256k1 curve and the WebSocket protocol.
A Nostr “account” is basically a key pair. Others in the network refer to your account by your public key. Everything you post has a signature attached to it, signed by your private key. Others validate everything you post.
These signed messages are then propagated using relays. The relays are not trusted by design, so Nostr clients are expected to validate the signatures of every message they care about.