they are vids that violate youtube's and other video site's TOS that havent been deleted YET. Another good site is
http://tubemall.net/daily.php , when youtube takes a vid down it is still stored on their servers for a day or so and this site lets you get at them. So if you see a deleted vid try getting at it with the site, it also lets you see what everyone else has entered in for the day. I think it clears the record at 12am eastern time, to make room for the next day.