Explicit: Use this tag when a track has explicit content. If your album has even one explicit track, the entire album will be marked as Explicit.
Clean: Use this tag when a track is an edited version of the originally explicit track. Do not use the Clean tag for a track that is not an edited version.
None: Use this label when a track is neither explicit nor a clean version. Most tracks and albums will require no parental advisory tag and this value will be the default value in iTunes Producer.
Why is my album marked Explicit in the iTunes Store when some of the tracks were not delivered as Explicit in iTunes Producer?
Our policy is that if your album has just one explicit song, the entire album will be marked explicit. Classify your music correctly so we can play it on iTunes Radio. Only classify a song as clean if there is also an explicit version of that song.