The NIP 72 for Nostrum Protocol defines how to create moderated communities on Nostrum. It specifies a specific event for creating a community and another one for approving posts within it. The community definition includes the community name, description, image, and set of moderators. Additionally, this NIP specifies that any new post request can be considered as a post request for the community if it has the `a` tag added to it. Moderators may delete their approval of a post at any time using event deletions.

Link: https://github.com/nostr-protocol/nips/blob/master/72.md