Essentially just a person visiting your website. If you ask for a stumble they usually will just open your website in a browser, take a look around, and walk away. Still, it is traffic, but in my opinion not very good quality at all and probably not targetted.
Interesting concept. So when websites do this isn't it kind of a lie to say they have PR5 considering they got it all from stumbles? I mean where does this topic stand when it come to ethics and should it be allowed?
Actually you don't really get PR from your traffic statistics. It is more related to how many other websites have links to yours. So if you have 1000 backlinks on 1000 different websites that are all PR5 websites, you will have your PR boost drastically more than likely, even if they do not supply you with any traffic. I suppose all traffic is good traffic, but personally I pride myself in having a bigger conversion rate than simply the number of visitors who visit my sites. I know that almost every unique visitor I recieve probably has an interest in my product. Therefore, they are more likely to buy or stick around. Granted, getting traffic at all is half the battle to your website being successful. Thats why some people use stumbles, even if conversion rates probably aren't very high at all.
It's what happens after you've had a little too much to drink and you're trying to make it back to your place at 3am.