short for "bivouac", a camping spot usually made in a pinch and for but one night; bivies are usually low on shelter and high on austerity. A bivy sack is a weatherproof sack of sleeping-bag proportions.
An abbreviation of bivouac, which means to sleep outside without a tent. On big walls, climbers often bivy on small ledges or portaledges (the poor man's penthouse) hundreds or thousands of feet off the ground.