Bivy is short for ‘Bivouac’ which means “a temporary camp without tents or cover, used especially by soldiers or mountaineers”.
Other spellings include: Bivvy, Bivvi or Bivi.
A bivouac shelter is an improvised camp site or shelter; usually of a temporary nature, used especially by soldiers or persons engaged in scouting mountain climbers and survivalists.
A bivouac sack is a waterproof sleeping bag or personal sized tent typically used by climbers on multi-day excursions that do not want to carry a full size tent. This type temporary shelter can come in extremely handy for Bug Out Bags. Most Bivy sacks are made from light-weight, waterproof fabrics and add warmth. This is a great option for anyone who does not want to carry a full size tent or partake in Cowboy Camping.