Nostr: What are Nostr public and private keys?

Your public key identifies the signer of your events and is meant to be shared.

Short answer

Your public key identifies the signer of your events and is meant to be shared. Your private key signs events and must remain secret; anyone who obtains it can publish as you. Unlike a password for a hosted account, a Nostr private key is not something a relay can simply reset. Back it up securely before relying on it as a long-term identity.

Sources

NIP-01: Basic protocol, NIP-19: Human-readable encodings.