Geocaching is an outdoor activity in which the participants use a Global Positioning System (GPS) receiver or other navigational  techniques to hide and seek containers called "geocaches" or "caches" anywhere in the world. A typical cache is a small waterproof container usually a tupperware or ammo box containing a logbook. Larger containers can also contain items for trading, usually toys or trinkets of little value. Geocaching is most often described as a "game of high-tech hide and seek" sharing many aspects with orienteering, treasure-hunting, and waymarking.

Geocaches are currently placed in over 100 countries around the world and on all seven continents, including Antarctica. As of April 18, 2010, there are over 1,035,638 active geocaches around the world.

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. According to Dave Ulmer's message, the original stash was a black plastic bucket buried most of the way in the ground and contained software, videos, books, food, money, and a slingshot.