A Virtual Cache is a cache that exists in a form of a location. The reward for these caches is the location itself and sharing information about the visit. Because of the nature of these geocaches, the cache vistor is often required to take a picture or answer a question about the location before they can post. In addition, although many locations are interesting, a virtual cache should be out of the ordinary enough to warrant logging a visit.
Virtuals are now considered waymarks on Waymarking.com, though older Earthcaches that were created before the posting of the official waymarking website have been grandfathered into the geocaching website.