Sous vide literally means "under vacuum" in French and is a method of cooking in which food is sealed in airtight plastic bags then placed in a temperature-controlled water bath for anywhere between 1 to 48 hours. The main advantage of Sous vide is to get perfect internal cooking based on the temperature you set. Typically around 55°C to 60°C (131°F to 140°F) for meat and higher temperatures (but shorter cooking times) for vegetables.
Other advantages of Sous Vide are increased moisture and flavor retention as well as less seasoning required because all cooking is contained inside of the sealed bag. Once the Sous vide process is complete, the food is then seared or grilled for just a few seconds on high heat to brown the outside, with the inside still perfectly pink!
Sous Vide cookers are available in two styles, the portable versions which attach to any existing pot or GN tank or the self-contained units which have their own water tanks.