An interstitial ad is an advertisement put in between content - the welcome.html that was on TechCrunch today was an ad greeting ALL users of techcrunch with a little "click here to see the website" at the top.<p>Defined -&#62; <a href="http://en.wikipedia.org/wiki/Interstitial_webpage" rel="nofollow">http://en.wikipedia.org/wiki/Interstitial_webpage</a>