Sport originally derived from sport climbing, consisting in short sequences of "moves" (movements of the arms allowing the body to be moved up a climbing wall, a rock boulder or even a house wall) that requires huge levels of
strenght on the forearms & fingers, and different special tecniques. This sequence is normally called a "problem". The
climber is not
roped, and the only protection allowed is a thick
foam mattress called "crashpad".
Bouldering problems rarely go higher than 3 or 4 meters above the ground.
"Solving" a problems often forces to make unlikely movements, like "pinching" a hold with your heels, or literally jumping from hold to hold (doing a "
dyno"). Style is important, but what really counts is to reach the last hold (the "top")
Bouldering was developed in the 60's in France and in California (by
John Gill, the "
human fly") as a pastime for bored rock climbers in off-season. In the 90's, however, the growth of indoor climbing walls (often homemade) and
rock climbing gyms has made
bouldering popular with the urban / hip-hop crowd, transforming it - in France and UK - in a "signature" sport like skateboarding. Part of the popularity of bouldering is due to the fact that it's being quite cheap - the only thing you need is a pair of climbing shoes (and the crashpad if you're bouldering outdoor).
There's a lively competition circuit around the world, and there are now bouldering sites (often simple concrete walls) almost in every city of the world. In fact, bouldering is now more a urban sport than an outdoor activity.