Meaning of 101 ?

Hey,
Just a question: What the heck does the 101 mean in the metal scene ? I see it appear everywhere, but I just can't decipher it's meaning. If anyone could tell me, I'm dying to know :) It's probably something obvious so don't kill me for not knowing.

Latz, Gul.

It means the basics of something. Just like in school.

Exemple : Physics 101 means your first class in physics.

So when you see Metal riffs 101, it means that your going to talk about the basics of metal riffs.

like 101 dalmatians is about dog training.