Simply put, geocaching is treasure hunting for the 21st century. Armed with a GPS receiver, a set of coordinates that tell you the location of a cache, and a healthy sense of adventure, players go out and look for caches of goodies hidden by other geocachers. If one of the goodies in the cache strikes your fancy, you can take it–provided you leave another goodie in its place. In addition to the goodies, caches nearly always contain a log book of some sort so that you can record your thoughts and scribble a note for future cache visitors.
Buxley’s Geocaching Waypoint