Came across these interesting terms in this site http://www.adventuresportsonline.com/mtbterms.htm
Bagging a Peak: Making it to the summit of a mountain.
Bagging Out: Canceling a ride
Bagger: A person that habitually bags out. Also known as a loser.
Basecamp rides: Setting up camp and using it as the start and finish of tours.
Bonk: Reaching the point of exhaustion.
Dab: Taking your foot off the pedal and touching the ground.
Doubletrack: Overgrown road that is like two parallel trails.
Endo: Going over the handlebars.
Flash: Clearing a technical pitch without dabbing.
Gnarly: An 80's term for a particular steep and rough section of trail.
Gonzo: Riding with reckless abandon. Not generally appropriate for singletrack.
Hammer: Someone in great shape, who goes all out most of the time.
Hard-tail: A bike without rear suspension.
Header: Going over the handlebars.
Kicker: A steep section of road or trail.
O.D.: This is short for "Off Day". Even the best riders have them. It is important to recognize the symptoms and to back off when you arehaving an O.D.
Out and Back: Tour where the return is a retracing of the route in.
Over The Bars (OTB): Unexpected dismount over the handlebars.
Pitch: A short section of technical road or trail.
Pokes: Short for slow pokes. This is someone that always lingers in the back of the pack. This is not a crime.
Powder Run: Extremely dusty section of trail.
Rock Garden: Section of the trail that is completely covered with grapefruit (baby head) size to basketball sized rocks.
Semi-loop: Loop trip with a section of out and back attached.
Singletrack: Narrow trail.
Soft-tail: A fully suspended bike.
Technical route: Section of road or trail that is very demanding of bike handling skills.