A bivvy is a type of TENT that is lightweight and designed for camping in extreme weather conditions. It is usually made of waterproof material and is often used by hikers, climbers, and mountaineers. The term 'bivvy' is derived from the British military term 'BIVOUAC, ' which refers to a temporary shelter. Bivvies are typically smaller than traditional tents and provide less protection from the elements. They are also easier to set up and take down, making them ideal for short trips.