It’s a spec for Encrypted Private Messaging (i.e: DMs and small groups), a neat combo of a couple other NIPs that define the Encryption and Metadata hiding (Giftwrapping).

https://github.com/nostr-protocol/nips/blob/master/17.md

Much inspiration taken from nostr:npub1tm99pgz2lth724jeld6gzz6zv48zy6xp4n9xu5uqrwvx9km54qaqkkxn72, another brilliant NIP-17 client. 💚