A primary metadata source is a source for Artist, Title, and Source fields in a beatmap's metadata officially promoted by the song's artist or their label. 283u1s
An artist's website, their label's website, CD scans, and official s to websites like Bandcamp, YouTube, and SoundCloud are considered primary sources for beatmap metadata. Third party websites such as wikis, databases (vndb, vgmdb, etc.), and music services (Spotify, iTunes, Amazon, etc.) do not always reflect the artist's intention and should not be treated as primary sources.
Beatmaps aiming for Ranked status are required to use metadata from a primary source. See the ranking criteria for more rules and guidelines regarding beatmap metadata.