In the context of the World Wide Web, a gravesite is either:
1) A Web site that has been abandoned or forgotten by its originators that is nevertheless still accessible on a server. (There is a vast but untold number of these.) A synonym is ghost site.
2) A Web site that, in the eyes of marketers, has failed to get sufficient traffic to be interesting to advertisers or other revenue providers, possibly by not finding an audience niche or building an audience community, or by failing to find a distribution partner such as America Online, Yahoo, or Netscape.