A geocaching log is a record used in the pastime, or game, of geocaching. Geocaching is a modern-day scavenger hunt, or game of hide-and-seek, that uses a GPS to find the treasure or treasures in the hunt. As a result, these games are generally played on a much larger scale than their predecessors. A geocaching log, also known as a geocaching logbook, is generally a record of who reached the geocache, also known as a cache — the container that serves as the goal of the hunt. Caches typically hold the geocaching log and sometimes they will hold some trinkets for successful hunters. Online geocaching logbooks typically serve the purpose of reporting the failure to find a geocache.
Matt Stum coined the word geocaching in 2000 from geo meaning “Earth” and cache meaning “a spot for temporary storage.” The game, which depends on the use of the Global Positioning System (GPS), wasn't possible until 2000. Prior to 2000, GPS readings had only been accurate to 300 ft (91.44 m); this limitation was imposed for the purpose of military and government security. In 2000, however, the policy was changed, and readings became accurate, within a range of 6 to 20 ft (1.83 to 6.1 m).
Dave Ulmer, a GPS enthusiast, decided to test the quality of the new GPS. He hid a geocache, or cache, which was the hunt's treasure. Then he provided some instructions for others to follow in order to locate the geocache using GPS. In three days, two people had found it. The cache owner and the two seekers were the first three geocachers — people who create and search for geocaches.
As the pastime developed and spread, the geocaching log became an integral part of the process. In fact, sometimes a geocache consists only of the logbook, in which case, it may be referred to as a microcache. While the geocache prizes or trinkets, if included, are generally placed in a waterproof container, or sometimes a zip-top bag, it is recommended that the geocaching log be double-bagged for protection from the weather. In any case, the person who sets the geocache characteristically makes the first entry in the geocaching log, recording the coordinates of the cache, at minimum.
People who find a cache usually exchange a trinket or prize they have brought along with one they find in the cache and use the geocaching log to record the fact that they found the cache. They may also record details of their search and any compliments they have for the person who set it or problems they encountered in their search. There are some special acronyms used in geocaching logs. The person who is first to find the cache, represents this in their log entry with the acronym FTF. Those who want to thank the cache owner may abbreviate the phrase “thanks for the cache” as TFTC. Another acronym is used when a person doesn’t exchange a prize stands for “took nothing; left nothing,” abbreviated TNLN.
Some geocachers use online geocaching logs. These are particularly useful for recording the failure to find a geocache, which is indicated by the phrase “did not find” and abbreviated as the acronym DNF. A cache owner receiving such a message will generally check to see if the cache has been disturbed or removed.