As you begin to geocache, you will come across some terms that you need to know. Some terms are slang and other words are acronyms. A lot of the time these terms and acronyms are used in the on-line logs, so understanding what they mean will only help you in the long run. Let me give you a few examples.
FTF: First to Find. After a new cache is published, the first person to find it claims FTF honors. Cachers who love to go after FTF's are commonly called "FTF Hounds."
TFTC: acronym for Thanks For The Cache. Just a polite way to thank the cache owner for putting out the cache.
TFTH: acronym for Thanks For The Hide. Again, just a polite thank you on your log for the cache owner.
SWAG: acronym for Stuff We All Get. This is the little trade items you leave in caches for other cachers to take.
TNLN: acronym for Took Nothing Left Nothing. This lets other cachers know that you took nothing out of the cache and left nothing in the cache.
TNSL: acronym for Took Nothing Signed Log.
I just want to make a note here that it is a common courtesy to leave a swag item in a cache if you take a swag item. Some common SWAG items are coins, marbles, shells, patches, stickers, fancy pencils, legos, balls, magnets, and plastic animals. The more you cache, the more you'll get a feel of what people leave. I like to leave fishing bobbers and sea shells. I like to take foreign coins.
BYOP: acronym for Bring Your Own Pen. The cache owner will usually put this on the cache page to let you know that the cache container is too small to house a pen, so bring your own pen to sign the log.
DNF: acronym for Did Not Find. If you couldn't find a cache, you can go to the cache page and log a DNF. This just lets other cachers know it was difficult to find, or maybe even missing. If a cache gets several DNF's in a row, then the cache owner will have to go check to make sure the cache is still there.
GPS: this is for the GPS unit you own and use to find your caches.
CITO: acronym for Cache In Trash Out. This is an ongoing environmental effort to clean up as you cache. In other words, cache on your way in and stuff trash in a bag on your way out.
So there you have it. These are some of the most common terms that you will run across while caching. If you want to study up on more terms, please visit the official geocaching page at: