a commercial seen while watching a youtube or other video site video. Usually it plays before the video when the site is of a commercial nature, such as yahoo's launchcast music video site. The word is formed from the combined words of commercial and computer. AKA computer commercial. It can also be used for a commercial that is played on tv, but is made available online.
"I watched a compercial on pepsi.com"
"I just saw a cool compercial play while watching a Bad Religion music video on yahoo.com"