A ghost site is a Web site that is no longer maintained but that remains available for viewing. Since many sites don't identify their date of last update, it's not always easy to tell whether a site is a ghost site or just resting. A ghost site is not to be confused with a retired or invisible site (one which doesn't exist anymore and results in a "Not found" message). It's possible to have a ghost site that continues to be useful or appealing because its content doesn't date easily.
A ghost site that for some reason seems to have moved to another location is a zombie.