While some think of this term as merely their favorite
euphemism for
crash, it's actually more specific than that.
A CFIT incident is one in which an aircraft hits the ground (usually a mountain) without any structural failure or loss of pilot control. This normally happens under Instrument Meteorological Conditions -- that is, in clouds. People normally don't hit what they can see (although there are, of course, exceptions). Thus it specifically excludes mechanical failures, mistakes in piloting, and so forth.
A frequent cause of CFIT crashes is navigational error, especially errors in the programming of GPS-based systems.
As a result of a string of CFIT incidents in the early 1970's, the NTSB recommended that the FAA begin mandating the installation of Ground Proximity Warning Systems in all large passenger aircraft. The FAA has done so and incidents of CFIT among large US aircraft have decreased significantly. These regulations were extended to commuter aircraft with more than 10 seats on April 1, 1994. These regulations do not apply overseas, however, and they have not eliminated all CFIT accidents. Efforts like EGPWS (Enhanced Ground Proximity Warning System) and advanced terrain awareness and warning features of, for example, Highway In The Sky, and in various synthetic vision systems aim to further reduce CFIT rates.
Airbus Industries aircraft are (perhaps unjustifiably) particularly notorious for CFIT crashes, because their advanced fly-by-wire design makes them more susceptible, and prone, to programming errors.