What Exactly is Residual?

I was thinking about what my idea of residual is. In normal terms, it means receiving money over and over from work you performed once, like royalties from a product or something. My theory on the whole idea is that the money will eventually dwindle off from each venture, so you really have to keep busy coming up with new things. At first, you have to be really busy until you hit your income goal and can sort of go into a maintenance mode.

Is my vending considered residual? I mean, sort of and then again not. I have to fill them up and collect money, which is work I have to perform, but I no longer have to place a machine once it is placed. Finding locations is about 90% of the business anyway. I think I would place that under residual. Rental income is a type of residual income. Too bad I don't have anything to rent out. Royalties from writing, photography, and programming are feasible. I first need to learn to write and take pictures. Programming I can do, but what? Perhaps make an app for iphones and sell it on the istore. That is a possibility.

So far I have:
Vending
Royalties
Rental

But what about internet specific ventures? Id really like to focus on those. The main reason for this is the flexibility of location. I would hate to have to completely sell all ventures and restart them if I decided to move somewhere else. The idea of residual is continued income I know, but to make more you have to do more work, or replace the streams that dry up. I'd like to be able to do that while I am anywhere in the world. Wouldn't that be nice?