Abbreviations of trails abound. But here are some other words and terms (in no particular order) commonly used by long-distance hikers.
Thru-hiker: A hiker who will attempt to hike the complete trail in one go, or in one season.
Section hiker: A hiker who hikes a trail in small sections; he or she may not plan on completing the trail.
Trail Name: The catchy moniker a hiker chooses to go by for an extended hike. Examples are legion—Yogi, Vagabond, The Mad Viking, AWOL, Skittles, Dreamwalker, Hamlet (that’s me), etc. Choose a name before someone tags you with one you may not like.
Camel up: Quench your thirst; fill your water bottles.
Vitamin I: Ibuprofen, or similar pills to ease joint pain and treat other aches.
Gorp: Typically, a combination of mixed nuts, dry cereal, raisins, chocolate chips or candy bits, and such. Usually homemade and eaten from baggies. Designed to give quick energy. (Eat too much gorp and it will begin to taste like birdseed.)
TP: I saw this on everyone’s gear list and couldn’t figure it out. TP stands for Toilet Paper.
Bushwhack: Blaze your own trail
Flip-flop: Hike in one direction, then leap ahead by other means and hike in the opposite direction, back to the former spot. (used in dealing with snow, fires, bad weather)
Zero day: A no mileage day.
Trail angel: Anyone, usually a non-hiker, who helps a hiker—ride, food, a place to stay, etc.
Yogi: To not quite ask for food, but get it by looking hungry, forlorn—use your imagination.
For a comprehensive list of trail terminology, see Michelle Ray’s How To Hike the A.T.