Not Rated (Adult!): For searching, screening, and other Archive functions, this may get treated the same way as explicit-rated content. In reality, it could be anything from porn to completely family-friendly stuff. Choose this rating if you prefer not to rate your content (because you don't like ratings, because you're trying to avoid spoilers, etc.).
General Audiences: This content is suitable for anyone.
Teen And Up Audiences: The content may be inappropriate for audiences under 13.
Mature (Adult!): This is for content with adult themes (sex, violence, etc.) that isn't as graphic as explicit-rated content.
Explicit (Adult!): This is for porn, graphic violence, etc.