We think of a campaign as being a "niche." Each plan comes with a different amount of target URLs that you can build links to. Everything within a campaign shares a keyword research tab, so it's easier to think of them as niches and split them up that way. You can place any URL you want in a campaign and build links to that target. Including web 2.0 sites, YouTube videos or other sites that aren't your own, if you'd like to link build links to them you can. We also let you allocate different amounts of your credits to individual campaigns. If you want to focus more of your link building on a particular campaign or niche we make it easy to do.
In short, it's easier to think of a campaign as a niche and split them up that way. They're more of an organizational tool than anything else.