[randerson]

While the literal translation means "under vacuum", it is generally considered to refer to precise temperature control because that is the benefit of sous vide.

It is possible to sous vide without a vacuum bag in a steam oven, or in certain ovens with temperature probes.

[pdc56]

I second this. Precise temperature (with good conduction between the heat source and the food) and time.

I've cooked 'sous vide' under a running hot tap in a backpacker, which worked great. The water temp happened to be close to perfect (I have a method of measuring temperatures > 40c based on how long I can hold my hand under the running water before pulling out from the pain - surprisingly accurate).