Looking up the iTunes User Guide, it defines "Explicit" as
A label—issued by media producers—that alerts consumers to content that might be inappropriate for children.
So, it appears that they are going off the RIAA's definition of "Clean/Explicit"
Additionally, I was able to find a iTunes Users Guide for PC that goes into more detail:
Yes - you can sign in using different Apple ID for the music app and not share the same AppleID as you do with other items like the App Store, iCloud preferences, FaceTime and Messages. In fact, you could choose a different account for each one of the above if you wanted to be creative or difficult or just had specific needs.
I use my work AppleID for ...