I get this question a lot so here it is…
Geocaching (pronounced Geo-cashing) is a high-tech treasure hunt for gps users. Geocaches are hidden all over the world and the locations of these caches are posting on the internet. GPS users can then use the location coordinates to find the caches. These coordinates, along with other details of the location, are posted on a website. Once found, a cache may provide the visitor with a wide variety of rewards. All the visitor is asked to do is if they get something they should try to leave something for the cache. The finding geocachers record their exploits in the logbook and online.
Today, well over 480,000 geocaches are registered on various websites devoted to the sport.
Microcache hidden and found beside the Roman Colosseum
Typical cache treasures are not high in monetary value but may hold intrinsic value to the finder. Aside from the logbook, common cache contents are unusual coins or currency, small toys, ornamental buttons, CDs, or books. Also common are objects that are moved from cache to cache, such as Travel Bugs or Geocoins, whose travels may be logged and followed online. Occasionally, higher value items are included in geocaches, normally reserved for the “first finder”, or in locations which are harder to reach.
Geocaches can range in size from “microcaches,” too small to hold anything more than a tiny paper log, to those placed in five-gallon buckets or even larger containers.
If a geocache has been vandalized or stolen, it is said to have been “muggled” or “plundered.” The former term plays off the fact that those not familiar with geocaching are called “muggles”, a term borrowed from the Harry Potter series of books.
If a cacher discovers that a cache has been muggled, it can be logged as needing maintenance, which sends an e-mail to the cache owner so it can be repaired, replaced, or archived (deactivated).
The first documented placement of a GPS-located cache took place on May 3, 2000, by Dave Ulmer of Beavercreek, Oregon. The location was posted on the Usenet newsgroup sci.geo.satellite-nav. By May 6, 2000, it had been found twice and logged once.