What in the world is mlm?

WHAT IN THE WORLD IS MLM? OK, I see it all over the Internet but I'm new to the on-line working at home thing and I want to know about MLM. What is it and how it work ? How does one go about getting info on it ? It must be the best kept secert on the Internet because I can type in anything else that has to do with working from home and I get thousands of ways to do that job . Not MLM , tons of join MLM but nothing the really tells me what it is. I'm looking for something in black and white about what it is and how it works. So I can decide if it's something for me and others I know who are trying to just get started and we are stuck spending countless hours pounding away on our computers trying to find that one thing that is going to help us out. So please anyone if you know what MLM is let me know .Thank you