Cache Creep - The cumulative effect of geocachers returning a cache to a very slightly different position each time it is replaced. Over time, the cache "creeps" into an entirely different place.
CITO - Cache In Trash Out - When out geocaching, take a bag with you and pick up trash along the way!
Confluence - A confluence is defined as a flowing together; a meeting place (often of rivers). In our case a degree confluence is the exact spot where an integer degree of latitude and an integer degree of longitude meet.
Datum - A datum is something used as a basis for calculating and measuring. In the case of GPS, datums are different calculations for determining longitude and latitude for a given location. Geocaching uses the WGS84 datum for all caches.
FTF - First To Find. Usually found in the forums or written in the online or physical log books.
GPS - A system of satellites used for geocaching.
Haystacking - Hiding a cache in a place that has an exremely large number of possible hiding places.
Hitch hiker - A hitchhiker is an item that is placed in a cache, and has instructions to travel to other caches. Sometimes they have logbooks attached so you can log their travels. A Travel Bug and a Swaggie are examples.
Huckle Buckle Beanstalk! - What you call out when you are out finding caches with other teams, and you see and locate the cache before they do. It also confirms to Noobies that they are really out with loonies! this is an aboscure way to say you found it! - see this website for an explanation huckle buckle beanstalk
Letterboxing - Letterboxing is similar to Geocaching, but you use a series of clues to find a container. Once you find the container (or letterbox), you take a carved stamp from the box and stamp your personal logbook. You then take your carved stamp and stamp the letterbox's log book.
Spoiler - A spoiler is information that can give details away and ruin the experience of something. For example, telling someone the end of a movie before they see it. In geocaching, a spoiler gives away details of a cache location and can ruin the experience of the hunt.
TFTC - Thanks For The Cache , Alt. TFTH - Thanks For The Hunt.
TNLN - Took Nothing. Left Nothing. Usually found in cache logbooks for folks that enjoy the thrill of the hunt more than the material contents of the cache.
U,V & W
Virtual Cache - Adapted from "Virtual Reality," virtual means "nothing there." So a virtual cache means there is no cache container. It's the location that is the cache itself. Nothing is normally traded, except photos and experiences.