In geography, an oasis (plural: oases) or cienega (Southwestern United States) is an isolated area of vegetation in a desert, typically surrounding a spring or similar water source. Oases also provide habitat for animals and even humans if the area is big enough. The location of oases has been of critical importance for trade and transportation routes in desert areas; caravans must travel via oases so that supplies of water and food can be replenished. Thus, political or military control of an oasis has in many cases meant control of trade on a particular route. For example, the oases of Awjila, Ghadames, and Kufra, situated in modern-day Libya, have at various times been vital to both North-South and East-West trade in the Sahara Desert.

Oasis is an isolated area of vegetation in a desert.