Bouldering is a kind of rock climbing. It is climbing without rope and harness. It is climbing heights at which the climber does not usually suffer serious injuries in case of a drop. To protect from injuries there are usually special bouldering mats underneath the climber. It is usually practiced on large natural boulders and in climbing gyms.
Boulder routes are called "problems", because this style is like solving climbing-problems. The height of boulder problems is rarely higher than 3-5 meters. Otherwise the risk of injuries is too high. Often other climbers, who stand on the ground, spot the climbers to protect them from hitting the ground with the head or the spine.
Bouldering was invented in the late 19th century. It has been first documented in France, England and Switzerland. It has been practiced for a long time but in the 1930s and 1940s it was practiced for its own sake in Fontainebleau in France.
Today many rock climbers are specialized boulderers and it is their favourite style of climbing.