Hiking is an outdoor activity which consists of walking in natural environments, often on hiking trails. It is such a popular activity that there are numerous hiking organizations worldwide. The health benefits of different types of hiking have been confirmed in studies.
In the United States and United Kingdom, hiking refers to cross-country walking of a longer duration than a simple walk and usually over terrain where hiking boots are required. A day hike refers to a hike that can be completed in a single day, often applied to mountain hikes to a lake or summit, but not requiring an overnight camp, in which case the term backpacking is used.
Hiking a long-distance trail from end-to-end is also referred to as trekking and as thru-hiking in some places, for example on the Appalachian Trail (AT) or Long Trail (LT) in Vermont. The Long Trail is the oldest long-distance hiking trail in the United States. The Trans Canada Trail is the longest trail system in the world.
Hiking is one of the fundamental outdoor activities on which many others are based. Many beautiful places can only be reached overland by hiking, and enthusiasts regard hiking as the best way to see nature. Hikers see it as better than a tour in a vehicle of any kind, because the hiker's senses are not intruded upon by distractions such as windows, engine noise, airborne dust and fellow passengers. Hiking over long distances or over difficult terrain requires both the physical ability to do the hike and the knowledge of the route and its pitfalls.
Hikers often seek beautiful natural environments in which to hike. These environments are often fragile: hikers may accidentally destroy the environment that they enjoy. While the action of an individual may not strongly affect the environment, the mass effect of a large number of hikers can degrade the environment. For example, gathering wood in an alpine area to start a fire may be harmless if done once (except for wildfire risk). Years of gathering wood, however, can strip an alpine area of valuable nutrients. Generally, protected areas such as parks have regulations in place to protect the environment. If hikers follow such regulations, their impact can be minimized. Such regulations include forbidding wood fires, restricting camping to established camp sites, disposing or packing out fecal matter, imposing a quota on the number of hikers per mile.
Many hikers espouse the philosophy of Leave No Trace: hiking in a way such that future hikers cannot detect the presence of previous hikers. Practitioners of this philosophy obey its strictures, even in the absence of area regulations. Followers of this practice follow strict practices on dealing with food waste, human waste, food packaging, and alterations to the surrounding environment.
There is one situation where an individual hiker can make a large impact on an ecosystem: inadvertently starting a wildfire. For example, in 2005, a Czech backpacker burned 7% of Torres del Paine National Park in Chile by knocking over an illegal gas portable stove. Obeying area regulations and setting up cooking devices on designated areas (or if necessary on bare ground) will reduce the risk of wildfire.
Hiking may produce threats to personal safety. These threats can be dangerous circumstances while hiking and/or specific accidents or ailments. Diarrhea has been found to be the most common illness afflicting long-distance hikers in the United States.
Dangerous hiking circumstances include losing the way, inclement weather, hazardous terrain, or exacerbation of pre-existing medical conditions. Specific accidents include metabolic imbalances (such as dehydration or hypothermia), topical injuries (such as frostbite or sunburn), attacks by animals, or internal injuries (such as ankle sprain).