What do you people do?

[Violent Omelet]

Not intended to be rude, but I noticed the different levels of "moderator" around here and wondered exactly what duties were entrusted to which titles. I've searched the forums, but I haven't been able to find the answers I was looking for, so... I'm curious:

What is the difference between a "Sentry", a "Protector", a "Guardian", and an "Administrator"? What does each one do? Are there common duties entrusted to all four, and special duties separately assigned to each?

P.S.: If it's none of my business, I apologize in advance. Just very curious. I've rarely ever seen categorization like this before.