bivvy

A bivouac shelter is any of a variety of improvised camp site or shelter that is usually of a temporary nature, used especially by soldiers or persons engaged in scouting and mountain climbing. It may often refer to sleeping in the open with a bivouac sack, but it may also refer to a shelter constructed of natural materials like a structure of branches to form a frame, which is then covered with leaves, ferns, and similar material for waterproofing and duff (leaf litter) for insulation. Modern bivouacs often involve the use of one or two man tents, but may also be without tents or full cover. In modern mountaineering the nature of the bivouac shelter will depend on the level of preparedness; in particular whether existing camping and outdoor gear may be incorporated into the shelter. A bivouac shelter is colloquially known as a bivvy (also spelled bivy or bivvi or bivi).
The word bivouac is French and ultimately derives from an 18th-century Swiss German usage of beiwacht (bei by, wacht watch or patrol). It referred to an additional watch that would be maintained by a military or civilian force to increase vigilance at an encampment. Following use by the troops of the British Empire the term became also known as bivvy for short.

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