A hike is a long, vigorous walk, usually on trails or footpaths in the countryside. Walking for pleasure developed in Europe during the eighteenth century. Long hikes as part of a religious pilgrimage have existed for a much longer time. "Hiking" is the preferred term in Canada and the United States; the term "walking" is used in these regions for shorter, particularly urban walks. In the United Kingdom and Ireland, the word "walking" describes all forms of walking, whether it is a walk in the park or backpacking in the Alps. The word hiking is also often used in the UK, along with rambling, hillwalking, and fell walking (a term mostly used for hillwalking in northern England). The term bushwalking is endemic to Australia, having been adopted by the Sydney Bush Walkers Club in 1927. In New Zealand a long, vigorous walk or hike is called tramping. It is a popular activity with numerous hiking organizations worldwide, and studies suggest that all forms of walking have health benefits.

In the United States, Canada, Ireland, and the United Kingdom, hiking means walking outdoors on a trail, or off trail, for recreational purposes. A day hike refers to a hike that can be completed in a single day. However, in the United Kingdom, the word walking is also used, as well as rambling, while walking in mountainous areas is called hillwalking. In Northern England, Including the Lake District and Yorkshire Dales, fell walking describes hill or mountain walks, as fell is the common word for both features there.

Hiking sometimes involves bushwhacking and is sometimes referred to as such. This specifically refers to difficult walking through dense forest, undergrowth, or bushes where forward progress requires pushing vegetation aside. In extreme cases of bushwhacking, where the vegetation is so dense that human passage is impeded, a machete is used to clear a pathway. The Australian term bushwalking refers to both on and off-trail hiking. Common terms for hiking used by New Zealanders are tramping (particularly for overnight and longer trips), walking or bushwalking. Trekking is the preferred word used to describe multi-day hiking in the mountainous regions of India, Pakistan, Nepal, North America, South America, Iran, and the highlands of East Africa. Hiking a long-distance trail from end-to-end is also referred to as trekking and as thru-hiking in some places. In North America, multi-day hikes, usually with camping, are referred to as backpacking.

The poet Petrarch is frequently mentioned as an early example of someone hiking. Petrarch recounts that on April 26, 1336, with his brother and two servants, he climbed to the top of Mont Ventoux (1,912 meters (6,273 ft)), a feat which he undertook for recreation rather than necessity. The exploit is described in a celebrated letter addressed to his friend and confessor, the monk Dionigi di Borgo San Sepolcro, composed some time after the fact. However, some have suggested that Petrarch's climb was fictional.

Jakob Burckhardt, in The Civilization of the Renaissance in Italy (in German in 1860) declared Petrarch "a truly modern man", because of the significance of nature for his "receptive spirit"; even if he did not yet have the skill to describe nature. Petrarch's implication that he was the first to climb mountains for pleasure, and Burckhardt's insistence on Petrarch's sensitivity to nature have been often repeated since. There are also numerous references to Petrarch as an "alpinist", although Mont Ventoux is not a hard climb, and is not usually considered part of the Alps. This implicit claim of Petrarch and Burckhardt, that Petrarch was the first to climb a mountain for pleasure since antiquity, was disproven by Lynn Thorndike in 1943. Mount Ventoux was climbed by Jean Buridan, on his way to the papal court in Avignon before the year 1334, "in order to make some meteorological observations". There were ascents accomplished during the Middle Ages; Lynn Thorndike mentions that "a book on feeling for nature in Germany in the tenth and eleventh centuries, noted various ascents and descriptions of mountains from that period", and that "in the closing years of his life archbishop Anno II, Archbishop of Cologne (c. 1010 – 1075) climbed his beloved mountain oftener than usual".

Other early examples of individuals hiking or climbing mountains for pleasure include the Roman Emperor, Hadrian, who ascended Mount Etna during a return trip from Greece in 125 CE. In 1275, Peter III of Aragon claimed to have reached the summit of Pic du Canigou, a 9134-foot mountain located near the southern tip of France. The first ascent of any technical difficulty to be officially verified took place on June 26, 1492, when Antoine de Ville, a chamberlain and military engineer for Charles VIII, King of France, was ordered to ascend Mont Aiguille. Because ropes, ladders and iron hooks were used during the ascent, this event is widely recognized as being the birth of mountaineering. Conrad Gessner, a 16th Century physician, botanist and naturalist from Switzerland, is widely recognized as being the first person to hike and climb for sheer pleasure.

However, the idea of taking a walk in the countryside only really developed during the 18th century in Europe, and arose because of changing attitudes to the landscape and nature associated with the Romantic movement. In 1790 William Wordsworth set off on an extended tour of France, Switzerland, and Germany, which he describes in his autobiographical poem The Prelude (1850). Walking tours were popular in the 19th century, In earlier times walking generally indicated poverty and was also associated with vagrancy. In previous centuries long walks were undertaken as part of religious pilgrimages and this tradition continues throughout the world.

In earlier times people mainly hiked for practical reasons, or on religious pilgrimages. Numerous modern hiking trail follow such ancient routes. The British National Trail the North Downs Way closely follows that of the Pilgrims' Way to Canterbury.