Like any specialised field, trail running and ultrarunning are full of strange terms that are quite perplexing to the beginner. Some of them are even perplexing to the experienced trail runner. Here is a collection of some of the jargon I've come across in my travels with the trail running community. Some of these are also used by non-trail runners.
Aid station (also drink station, checkpoint): A table or shelter positioned along a race course, and attended to by volunteers. Water, and sometimes food and medical facilities may be supplied.
Bonk: Suffer from extreme exhaustion due to depleted glycogen stores.
Buff: A versatile one-piece cloth band that wraps around the head, neck, wrist, and is useful for soaking up sweat, providing sun protection, and keeping hair under control.
Cadence: Number of steps per minute.
Crew: The group of people who support a runner during race.
Cutoff times: If you don’t make it to an aid station by a certain time, you will not be allowed to continue the race.
DNF: Did not finish.
DNS: Did not start.
DOMS: Delayed onset muscle soreness.
Drop bag: A bag to back various supplies that you might need during a race. These are transported by race officials to designated aid stations and will be availav=ble for you to use when you get there.
Fartlek: Swedish for "speed play". A running workout in which the pace is varied, combining a mixture of fast, slow and moderate pace.
Fire trail: A wide, smooth trail, including dirt roads used by service vehicles.
FKT: Fastest known time.
Gaiters: Protective piece of cloth, fixed around the ankle to stop dirt and rocks entering the shoe.
Hiking poles: Sticks used by hikers and runners to provide extra support on the trails.
Junk miles: Long, slow runs.
Lugs: Bits of rubber on the outsole of a trail shoe. Their function is to provide traction.
Midsole: The area of the shoe between the upper and outsole that's
primarily responsible for the shoe's cushioning. Most midsoles are made
Negative splits: Running the second half of a race faster than the first half.
Out and back: When a course head to a point, then turns around and head back to the starting point.
Outsole: The material on the bottom of a running shoe, usually made of durable rubber.
Single-track: A narrow trail, only wide enough for a single person. These are sometimes used by mountain bikers, so be careful.
Snot rocket: Blowing snot from your nose by closing one nostril with a finger and blowing forcefully out of the other.
Strides: Short, fast, but controlled runs of 50 to 150 meters.
Taper: Reducing the amount or intensity of running prior to a race in order to ensure peak performance.
Technical: Uneven or steep terrain with numerous obstacles on which running is very difficult.
Toebox: The front portion of a shoe, where the toes go.
Ultramarathon: Any distance longer than a marathon (42.2km, 26.2mi).
Upper: The material on the top of the shoe.
Vest: Very lightweight backpack used to carry water, food and supplies.
Let me know in the comments if I've forgotten any.