An outdoor activity wherein a backpacker packs all of his or her gear into a backpack. This gear must include food, water, and shelter, or the means to obtain them, but very little else, and often in a more compact and simpler form than one would use for stationary camping. A backpacking trip must include at least one overnight stay in the wilderness (otherwise it is a day hike). Many backpacking trips last just a weekend (one or two nights), but long-distance expeditions may last weeks or months, sometimes aided by planned food and supply drops.

Backpacking camps are more spartan than ordinary camps. In areas that experience a regular traffic of backpackers, a hike-in camp might have a fire ring and a small wooden bulletin board with a map and some warning or information signs. Many hike-in camps are no more than level patches of ground without scrub or underbrush. In very remote areas, established camps do not exist at all, and travelers must choose appropriate camps themselves.

In some places, backpackers have access to lodging that is more substantial than a tent. In the more remote parts of Great Britain, bothies exist to provide simple (free) accommodation for backpackers. Another example is the High Sierra Camps in Yosemite National Park. Mountain huts provide similar accommodation in other countries, so being a member of a mountain hut organization is advantageous (perhaps required) to make use of their facilities. On other trails (e.g. the Appalachian Trail) there are somewhat more established shelters of a sort that offer a place for weary hikers to spend the night without needing to set up a tent.

Most backpackers purposely try to avoid impacting on the land through which they travel. This includes following established trails as much as possible, not removing anything, and not leaving residue in the backcountry. The Leave No Trace movement offers a set of guidelines for low-impact backpacking ("Leave nothing but footprints. Take nothing but photos. Kill nothing but time. Keep nothing but memories").

Professional backpacking
For some people, backpacking is a necessary and integral part of their job.

In the US military a framed backpack is referred to as a "rucksack" or simply a "ruck". Soldiers who serve in the militaries of most nation-states usually receive at least some rudimentary backpacking training while infantrymen are often trained to a more advanced backpacking skill level. They share many common attributes with amateur backpackers: being self-contained, use of land-navigation skills and actively minimizing their environmental foot-print. There are, however, a few differences—such as the need to carry weapons, ammunition, and communication equipment, and sometimes the need to maintain "noise and light discipline", which means remaining silent and in darkness to avoid detection.

Other professional backpackers include scientific and academic researchers, professional guides, photographers, park-rangers and "search & rescue" personnel.

Motivation
People are drawn to backpacking primarily for recreation, to explore places that they consider beautiful and fascinating, many of which cannot be accessed in any other way. A backpacker can travel deeper into remote areas, away from people and their effects, than a day-hiker can. However, backpacking presents more advantages besides distance of travel. Many weekend trips cover routes that could be hiked in a single day, but people choose to backpack them anyway, for the experience of staying overnight.

These possibilities come with disadvantages. The weight of a pack, laden with supplies and gear, forces traditional backpackers to travel more slowly than day-hikers would, and it can become a nuisance and a distraction from enjoying the scenery. In addition, camp chores (such as pitching camp, breaking camp, and cooking) can easily consume several hours every day. However, with practice, much of this downtime can be removed from the day.

Backpackers face many risks, including adverse weather, difficult terrain, treacherous river crossings, and hungry or unpredictable animals (although the perceived danger from wild animals usually greatly exceeds the true risk). They are subject to illnesses, which run the gamut from simple dehydration to heat exhaustion, hypothermia, altitude sickness, physical injury, and giardiasis. The remoteness of backpacking locations exacerbates any mishap. However, these hazards do not deter backpackers who are properly prepared. Some simply accept danger as a risk that they must endure if they want to backpack; for others, the potential dangers actually enhance the allure of the wilderness.

Equipment
The basic elements for maintaining human life in comfort are all carried while backpacking: shelter from "the elements," a system for sleep (bag and perhaps a pad), clothing (typical urban gear suffices for the most part), proper footwear, food and means to prepare it, and other smaller miscellany, some critical and some not. Almost all backpackers seek to minimize the weight and bulk of gear carried. A lighter pack causes less fatigue, injury and soreness, and allows the backpacker to travel longer distances. Every piece of equipment is evaluated for a balance of utility versus weight. Significant reductions in weight can usually be achieved with little sacrifice in equipment utility, though very lightweight equipment can be significantly more costly.

A large industry has developed to provide lightweight gear and food for backpackers. The gear includes the backpacks themselves, as well as ordinary camping equipment modified to reduce the weight, by either reducing the size, reducing the durability, or using lighter materials such as special plastics, alloys of aluminium, titanium, composite materials, impregnated fabrics and carbon fiber. Designers of portable stoves and tents have been particularly ingenious. Homemade gear is common too, such as the beverage-can stove.

Some backpackers use lighter and more compact gear than do others. The most radical measures taken in this regard are sometimes called ultralight backpacking.

Due to the emphasis on weight reduction, a practical joke common in some circles is to secretly pack a small but relatively heavy luxury item, such as a soft drink, into another backpacker's pack. Then, once the group stops for a rest, the perpetrator retrieves the item, thanks the bearer for carrying it, and consumes it.

Skills and safety
Survival skills are handy for peace of mind: In case the weather, terrain or environment is more challenging than prepared for.

Navigation and orienteering are useful to find the trailhead, then find and follow a route to a desired sequence of destinations, and then an exit. In case of disorientation, orienteering skills are important to determine where you are and formulate a route to somewhere more desirable. At their most basic, navigation skills allow you to choose the correct sequence of trails to follow.

First aid: effectively dealing with minor injuries (splinters, punctures, sprains) is considered by many a fundamental backcountry skill. More subtle, but maybe even more important, is recognizing and promptly treating hypothermia, heat stroke, dehydration and hypoxia, as these are rarely encountered in daily life.

Leave No Trace is the backpacker's version of the golden rule: To have beautiful and pristine places to enjoy, help make them. At a minimum, don't make them worse.

Distress signaling is a skill of last resort.