intermercial

from The Free On-line Dictionary of Computing (8 July 2008)

interstitial
intermercial
transition ad

   <World-Wide Web> A {World-Wide Web} page that appears before
   the expected content page.  Interstitials can be used for
   advertising (intermercial, transition ad) or to confirm that
   the user is old enough to view the requested page, etc..

   (2003-07-11)