Sous-vide (French for "under vacuum") is a method of cooking in which food is sealed in airtight plastic bag then placed in a water bath for longer than normal cooking time, 96 hours or more, in some case, at an exact temperature much lower than normally used for cooking, typically around 55 °C (131 °F) to 60 °C (140 °F) for meat and higher for vegetables. This is so the items cook evenly, ensuring that the inside is properly cooked without overcooking the outside, and retain moisture.
in 1799, Sir Benjamin Thompson first came up with this method of cook, he used air as a heat transfer method. it was later re discovered in the 1960s by american and french engineers and was used as a food preservation method.
The invention of the vacuum is also quite amazing. Once a food item is vacuum sealed it can last longer on the shelf or in the refrigerator because all the oxygen is removed, which is a major component in food oxidizing.
The sous vide method was adopted by Georges Pralus in 1974. He found that when he used this method to cook foie gras it would keep its original appearance and did not lose any amount of fat and had a better texture.
One limitation of sous vide cooking is the fact that it cannot have any kind of maillard reaction. Although some chefs will cook a something sous vide and then finish on the grill on high heat for that browning crust.
Some chefs might see this method of cooking as a cheat, and in some cases they are right. A true chef should know all the classic ways of cooking before tampering with the sous vide method.
