The hobby geocaching got its name in 2000 from suggestions on the gpsstash email list. As that origin suggests, it was called gpsstashing for the month it existed before being renamed. Geocaching echoes the longstanding hobby of letterboxing, the practice of leaving a letter (later a notebook) inside a box along a hiking trail and publishing clues pointing to its location. Geocache is from ancient Greek γεω- (geō-), meaning “earth”, and English cache, borrowed from French Canadian fur trappers in 1797. French cache is the noun form of cacher, meaning “to hide”.

The hobby’s date of origin can be explained by Blue Switch Day. On May 2, 2000, the accuracy of civilian GPS receivers increased from within about 100m to within about 10m, close enough that it became practical to search the entire 10m area for a cache. The first geocache was hidden on May 3, 2000. Civilian GPS receivers had been available since 1988 as a separate device and had become common among outdoor hobbyists in the 1990s, but trying to find an object within a 100m area was not a fun prospect.

Civilian GPS receivers were first made available after a tragic 1983 plane crash where a Korean passenger jet veered so far off course that it entered Soviet airspace and was shot down by a missile. It’s wild to think that a multimillion-dollar jet airplane would have no way to accurately determine its location just 42 years ago. GPS is a US military project that began operation in 1978. The 100m error in civilian GPS receivers was deliberately inserted by the US military from their introduction in 1988 until Blue Switch Day in 2000, to deter adversaries from buying civilian receivers and using their own system against them. The generic term for a satellite navigation system is satnav. The second satnav system was the Soviet GLONASS, which launched in 1982. Additional satnavs are currently operated by the EU, China, India, and Japan.