Geocaching is a hobby where someone hides a cache, or a box, and then lists it's coordinates on a website dedicated to geocaching. Other people will go to this site and get the coordinates and try to find it using a GPS. After finding the cache there is usually a paper to sign and then register online that you have found it. I find it interesting to trade trinkets that are left inside of these caches. If you go to geocaching.com it will give you more info.