The words “sous vide” literally translate to “under vacuum”, but it's the meaning behind the words that matters. For instance, sauté is from the French, “to jump,” but the technique doesn't strictly require aerobics, fun as they are. So, the question we must answer is, “If your food isn't 'under vacuum', is it still being cooked sous vide?” Yes.
Sous vide cooking is defined first and foremost by cooking at a precisely controlled temperature, typically at or slightly above the temperature you want the core of your food to reach. Although cooking in a sealed bag in a water bath is a common way to cook sous vide, it's not the only way.
There are lots of accepted sous vide scenarios that don't involve a bag at all. A favorite technique among sous vide enthusiasts is to cook whole eggs right in their shell, where nature has done the packaging for us. American chef Thomas Keller famously poaches lobster tails directly in a bath of circulating butter. Neither scenario involves vacuum bagging, but the results are unmistakably sous vide.
Because we're using the oven to cook foods using precise temperature and humidity control for edge-to-edge even doneness, we are going to go ahead and call it sous vide. Precision is, after all, the hallmark of this style of cooking.
