The NIP (Nostrum Improvement Proposal) 38 is a proposal that allows users to share their current status with others using the Nipper protocol. This includes what music they're listening to and what they're doing at the moment. The `kind` parameter is used to specify the type of status being shared. Two common status types are defined: `general` and `music`. `general` represent general statuses such as "Working", "Hiking", etc. `music` status events are for live streaming what you are currently listening to. The expiry of the `music` status should be when the track will stop playing. Any other status types can be used but they are not defined by this NIP. The status MAY include an `r`, `p`, `e` or `a` tag linking to a URL, profile, note, or parameterized replaceable event.

Link: https://github.com/nostr-protocol/nips/blob/master/38.md