Used when a post is sourced from a party that has some connection to the the original artist or (official) source provider. Examples include when commissioners upload what they've commissioned online (unless the Danbooru uploader in question is said commissioner, in which case commissioner upload is used instead; or if the commissioner made edits to the art), when artists send/submit their art to other accounts on sites such as Tumblr or Twitter (whether for fun, or as a gift), or when collaborating artists post each other's work.