What is a "stumble"?

Can someone explain to me exactly what a "Stumble" is? (like in this thread http://forums.digitalpoint.com/showthread.php?t=634474) I know it uses StumbleUpon, but I'm curious as to what it is.

 

using the stumbleupon tool bar you can choose if you like or if you don't like the site.

basically you visit the site, and press i like this site on the tool bar. thats considered as a stumble.

 

Thanks for the explanation Lethal7. Much appreciated.

 

I think it's better to say "I thumbs uppled your site," since the main concept of stumbleupon is stumbling from site to site. I bet many stumble exchanges are for naught, since when you sign up for stumble, the most logical meaning for stumbling is randomly browsing via the tool bar. But we being lazy linguists, can't be bothered with saying something like "I gave you a thumbs up on stumbleupon."

 

Yea just visit the site and you will see.