Neologism. It describes unusual fetishes, beliefs and activities that have been either developed on, or entirely facilitated by, the Internet. Something described as webcest should not simply be bizarre or unusual, but disturbing and unacceptable to most people (as incest is outside of the internet.)
Webcest is that special feelin' you get when you're makin' love to your old lady and you're both dressed like giraffes! It's that feelin' you get when you got high-res, glossy printouts of tubgirl and Goatse.cx and you're all alone on a school bus.