Riders fall into fairly 'different' groups in some respects, with some fairly 'different' terms describing, for example, what they do, what they do it on, where they can be found. Through this site you might find some of these terms you are not sure of. If so flick back here and hopefully you will find a definition.
Cross Country: Like the name suggests, crossing countryside, up and down. Just riding really.
Trail Riding: Just Cross Country with a less racy, more recreational tag. Use: 'that was a nice trail'.
Trails: Trails can also be a jump spot, rather than a flowing cross country trail. Use: 'Those trails have really sketchy kickers'. Sorry to confuse things.
Trials: All the same letters as trails, but very different. Very skilled riding over obstacles. Usually slow speed and very precise. Illogical, but then lots of good things are.
Dirt Jumping: As trails (2), hitting lumps of dirt and styling off them. Like trials, Illogical but good.
Downhill: Riding downhill, obviously. Generally pushing or gondola/shuttle access, best on a burly suspension bike. If you are put off the over specific title, then you might just be a free-rider.
Free-ride: Things get complicated here, Free-ride describes many things to many people, but generally means doing things how you like them, in a non competitive way. That usually means tighter more technical trails, focussing on features, either natural or man made. So it could be riding rock features, wooden bridges, dropping cliffs, hitting jumps. Just informal down-hilling. However it could also be riding technical cross country trails, or just about any thing else. Free-riding is what we all do, but has been given a trendy marketing title. Jump on the bandwagon!
4 Cross: 4 man riding downhill over a short course with big jumps and bermed corners.
Street Riding: For people who cannot get to proper trails because their jeans are too baggy. Riding steps, walls, banks, skate parks etc. in an urban environment.
BMX: Bicycle Moto X. Park, Pipe, Street Track or Dirt on a small bike, going big.
Cross Country Bike: Traditional bike for riding, all over the place.
Trail Bike: As above, but maybe a bit stronger and more stable.
Trials Bike: Tiny, strong and light, built to be nimble but to take abuse hopping and dropping about the place.
Jump Bike: Tiny, strong and heavy, built to be to flicky for style, but to take abuse landing hard.
Downhill Bike: Built for going down. Rubbish at going up. Maybe 6 to 10 inches of suspension travel. Very fast when pointing in the right direction.
Freeride Bike: Built for going down. Hopefully ok at going up as well. See riding styles definition for a lesser understanding.
4 Cross Bike: Like a jump bike. Maybe a bit lighter and more racy.
Street Bike: Just a Jump or Trials or BMX bike I suppose.
BMX: Usually small 20 inch wheels. Very small and strong. Different types available for different uses.
Berms: Banked corners that allow riders to hold more speed through turns
Rock Garden: Rocky section of trail that riders have to pick lines through.
Boulder Field: Lots of loose rock.
Slab Rock: Big rock, part of the hillside.
Doubles: Jump with a take off and landing with a gap in the middle to clear.
Table Top: Jump with a flat top rather than gap in the middle, so safer and easier.
Hip Jump: Kinked jump where the rider must change direction into the landing mid air.
Whoops: Mini sized jumps that riders can roll, manual (on the back wheel) or jump across.
Step-down: Jump where riders jump down into a landing lower down the hill.
Step-up: opposite of step down.
Drop-off: Feature where trail stops suddenly so rider must drop down to ride on. Usually off rocks and logs.
North Shore: Style of trail coming from the North Shore of Vancouver, typically using wooden ladders to link trail across difficult ground.
Park: Skate park incorporate rails, boxes, benches and ramps.
Pipe: Skate style quarter or half pipe ramp.
Fun Box: Skate style feature, with ramps leading up onto a box that riders can use as base for tricks.
Wall Ride: Trail that kicks up into a vertical or near vertical wall that riders push sideways into to stop falling down off. Usually either natural rock face or man made rock or wood wall.
Spine: Long raised 'spine' of dirt or concrete that riders use to pull different moves off.
Switchback: tight 180 degree corner.
Stone Pitching: man made trail surface using tightly wedged rocks to minimise erosion on vulnerable ground.
Hard-pack: tough packed down trail surface.
Single-track: The holy grail to many, good single track is magic. Skinny lines of dirt, focus needed.
Double-track: frowned upon by many, bad double track is boring. Forest roads etc, patience needed. Good for linking single-track though.
Mud: A necessary evil.
Dust: A rare wonder.
The Best Trail: A myth. If anyone makes this claim they are wrong, there is always better somewhere.