Power level explanations?

So, I usually spend a lot of time on battle forums for the sake of entertainment and interesting battles (duh) but I always find my self confused on power levels of characters. I see the titles tossed around a lot and don't fully grasp the concept of them.

I know of the classes Celestial, Skyfather, Herald, Street, etc. my question is what defines that?

To my understanding Celestial (under Presence and TOAA) are the strongest class Skyfather being second and so on and so forth. My question to you, viners are....

• Where did this class system come from?
• How is it rated?
• What defines a hero as a certain class?
• What powers must a hero have to be considered that class?
• What feats?
• What are all the classes in order?

Bump

The names come from characters of the same name.

• Celestial - Usually means general Cosmic, or levels of the Celestials.
• Skyfather refers to the rulers of pantheons. Usually: Zeus, Odin, etc.
• Herald - Around the level of one of Galactus' Heralds. Not necessarily Silver Surfer level, but around that.
• Street - Self-explanatory. No superpowers.

http://www.comicvine.com/cross-company-character-rankings/4015-43598/

@jedixman: Appreciate it!