Berm:  A banked corner that helps riders turn faster.

Biff: An equipment damaging contact with minimal results, and little or no physical injury. Comments: Can be accomplished without a machine.

Big Air:  Putting lots of air between yourself and the ground while jumping. 

Bottoming Out:  When you jump or get air and you land on your front wheel and this usually makes your shocks go all the way down.  If it happens you will know.

Checkpoint:  One or more points in a race course where it is verified that the rider has passed through that point.  Reduces cheating (in theory).

Class:  Grouping of similar riders.  Can be based on age, bike size, gender, skill, or some combination thereof.

DNF:  Did not finish.

Double:  Two jumps close enough together that an experienced rider can clear both in one jump.

Eat (ate) it: When you fall down and get dirt(ect) in your face. "Woah. i almost ate it on that jump"

Endo or End-o:  It's a funny way to get off the bike, unless performed by someone you know and like.  The bike goes "end over end" and the rider takes a trip over the handlebars.    It's a funny way to get off the bike, unless performed by someone you know and like.  The bike goes "end over end" and the rider takes a trip over the handlebars. 

Fat Air: Fat air means when u hit a jump at high speed and get alot of hight (did u see that fat air she just got)

Flying W: Hands on the handlebars, feet in the air, knees bent so that the body resembles a "W". Some do it on purpose, others, well, you're not always in control out there.

Getting air:  Both wheels off the ground.

Greasing:  Slang term used to tease freinds when they crash while landing or turning in a hair pin. ex- "dude u totaly greased that landiing, dude that grease in the hair pin was painful."

High-side:  Falling off the painful side of the bike.  Also defined as being in front of the bike and possibly having it land on you.

Low down:  While in the air laying flat against the bike and then releasing your hands from the handlebars.

Monkey Butt:  That rear-end feeling you get after you have ridden miles of trails.

Nac-Nac:  A trick performed while airborne in which the legs are positioned and extended out on the same side of the bike.

Obstacle:  Large or difficult hill, off-camber turn, extremely sharp turn, jump, rocks, whoops, rolling terrain/rises, brush, creek crossings, etc.

On the step, good clip:  Going really fast.  i.e. "that guy hit that at a good clip"

ORV/OHV:  Off-Road or Off-Highway vehicle.

OTB:  Over the bars.

Panic Rev:  Usually associated with revved up two-strokes. Throttle twisted WFO and tackling or charging whatever obstacle is in your way, be it from mother nature or a fellow racer.  Also used to intimidate slower racers. 

Pit stop:  An optional break during a race when a rider stops for gas, goggles, repairs, water, rest, sympathy, etc.

Power Band: When you pull the clutch and it gives the bike alot of power!

Power Shift: the act of shifting without using the clutch. You can shift faster by doing this, but really mess up your clutch

Putting someone in the weeds:  a non-contact action; Generally used either while passing another rider or preventing someone from passing you; A rider is forced to take such a lousy line that they exit the track. To do that cleanly, the put-er just has to get to the good line before the put-ee, and make sure that the put-ee can't get it back. 

Quick-fill:  A specialized gas container used to quickly fill a gas tank

Ragdoll: When someone crashes really bad (usually at a fast rate of speed) and the way thier bodies and limbs just flip-flop,and bounce through the air over and over just as if they were a rag doll.

Regrip:  Instead of turning the throttle and ending up with your wrist bent, reach down first and then pull the throttle back so that your hand and wrist are in their original position yet the power is increased.

Roost:  1: That really cool wave of dirt, mud, rocks, sand, or any combination that you spit out behind you, often intentionally aimed at whoever's behind you.  2: That really crappy, painful, annoying, dangerous, frustrating wave of dirt, rocks, sand and mud that someone in front of you nails you with, often intentionally.
"Roost unto others as ye would have them roost unto you!"

Sandbagging:  Racing below your ability to avoid being advanced to a more competitive class.

Soil Sample: getting a face full of dirt

Spode:  A carefree person who exhibits one or more of the following traits:
clumsy/accident-prone
lazy about even the most basic maintenance
inexperienced/slow

Spooge:  The black, gross gunk that dribbles out of the end of your silencer because the bike is running too rich, the silencer needs to be repacked, or it's just a trait of your particular bike that never completely goes away

Squid:  A rider, usually a novice, who has trouble controlling their bike.  Their erratic and unpredictable lines make them difficult and dangerous to pass.

Squirrelly:  When you lose control of the bike for a second and the bike is sliding around on you. 

Stoppie: also know as indo, when a rider uses his front brake to raise the rear wheel off the ground.(usually requires you to lean foward).

Straightaway:  A section of track where you can shift into high gears with less severe changes of direction and varieties of obstacles (easy and difficult).

Styling:  Adding your own riding style - any show-off maneuver done on a motorbike. Did you see gal lay the bike over sideways on that jump? He was really styling!

Technical:  A section of track with difficult obstacles that have to be taken at low speed.

Tight: Something that is done with style and is realyy cool. Like that new track is tight.

Tight Track:  A need for low gears, lots of close-together 90-degree-plus turns through tree sections.

Top End:
1) Top part of the motor - the piston and ring housed by the cylinder.
2) Replacing the piston and ring.  Done frequently on racing bikes.

Whoop-de-dos:  A series of bumps of varying height and spacing.