"This NIP defines the creation of NUDs: Nostr Unofficial Documents, which are descriptions of standards and sub-standards that do not pertain to this NIPs repo.

Anyone can create a NUD and they are immediatelly valid as soon as they are published. NUDs have owners and can be modified by these owners at any time, but they can also be forked or reinterpreted by others. However as implementations of these specs mature they will naturally coalesce into some accepted definition and it won't be possible for anyone to change that anymore in practice (even if they change the document, the Schelling point will just move to some other document or other set of documents).

NUDs are defined as NIP-54 kind:30818 events.

They should have a d tag starting with "nud:" followed by a succinct and identifiable name so they can be referred to in other contexts."

https://github.com/nostr-protocol/nips/blob/nuds/71.md