MLM's as we all most know pay out a "commission" over multiple levels. People that you personally didn't introduce can generate you income for the duration of them purchasing these products. So in other words every person that you introduce to the products and they purchase them over a period of time becomes residual income for you.

In the online marketing environment you also get Affiliate programs that makes use of a similar concept successfully. Multiple Tier affiliate programs has generated passive income for many people in the past and still is.

I have myself joined Golden Products, Sporttron and a couple of others over the years. It didn't work for me at all. To much hard work for to little profit. I have learned not to rely to much on other people to make me money though.