A climbing area is a small geographical region with a concentration of opportunities for climbing. The term is most commonly used of rock climbing areas, but there are also ice climbing areas that have the right combination of steepness and water to result in climbable ice during the winter.
While there are many mountains and cliffs in the world, only a small percentage are popular for climbing. Mountain ranges are frequently at high elevations, remote, and tend to have poor weather much of the time, which means that the climber spends more time hiking, camping, and battling the elements than actually climbing. At the opposite end of the scale, many cliffs are too small or the rock is too unstable to make for an enjoyable and safe experience.
An ideal climbing area has these qualities:
Yosemite Valley for instance is very nearly ideal. The valley is at a low elevation and allows climbing from March to November, it has an enormous amount of high-quality granite, with hundreds of routes ranging from the easy (The Grack) to some of the longest and hardest in the world, such as The Nose on El Capitan. As part of Yosemite National Park, the bases of the big walls are just a short walk from good roads, camping is available, hiking trails make the descents easy, and of course the scenery is world-class. Its main problem is that it's so popular that some routes will often have multiple parties of climbers getting in each other's way.
Most climbing areas fall short of the ideal, usually making up for it in some other way, sometimes just by being the closest good area to some city.
Since rock climbing became an activity distinct from mountaineering in the 20th century, it is usually possible to trace the entire history of an area, generally starting with a few local climbers using the area as "practice rocks" in preparation for mountaineering expeditions. Inevitably a few in the local community would become more interested in the area for its own sake, exploring the area for new and unusual routes, typically looking for a combination of challenge, safety, and elegance of line, the last being a subjective quality that is nevertheless easy for climbers to agree upon.
This process has become known as "development" of a climbing area, and, depending on the area, may include the placing of permanent bolts at key belays spots, rappel slings, as well as agreement on preferred equipment, minimization of environmental impact, and so forth, initially all done by word of mouth.
Development culminates in the publication of a climbing guidebook. The first edition of a guidebook may be little than a mimeographed pamphlet, but in the most highly developed areas, the books are thick tomes full of maps, photographs, and records of first ascents, and some have gone through multiple editions.
Climbers normally have a very light impact on an area; bolts are not visible from a distance, and only the knowledgeable will recognize the worn ground at the base of a route and the chalk residue on the rock for what they are. However, popular climbing areas eventually come to the attention of the area's legal stewards, whether they are the owners of private land, or the rangers of a park. In such cases, the local climbers may need to negotiate access rights or bolting policies. Places like Yosemite National Park actually have a staff of climbing rangers, who work with climbers to develop and enforce usage policies, and to perform rescues.