Bicycle trials is the sport of riding a bicycle through an obstacle course while not putting ones feet down. In competition scoring is based on the number of time a competitor puts a foot down (a dab). Usually the scoring works like this. If you put one foot or hand down, or against anything but your lower bike(pedals, wheels, etc.), you get one point. If you put two feet, a foot and a handlebar or seat, two hands, etc. you get five points. The person with the fewest points wins.
Obstacles include anything and everything that could possibly be ridden over. Cars, barrels, spools of cable, trees (sometimes still growing in the ground), etc. Moves used to get over them include the bunnyhop, the backhop, the ride up and many other moves.
Bicycle trials is a sport that requires many hours of practice. Most of the manouvres used can often seem impossible when first learning them. But the look on the faces of the uninitiated make it all worth it in the end.
And the Metanode
Here are all the writeups that I've found and written, so far, about bicycle trials. I try to keep this list up to date, but if you have any entries please message me.
Bunnyhopping (and the IMHO inferior bunny hop :-)
Norco Factory Trials Team
Kris Holm (Unicycle trials)