sous vide. Means "under vacuum". https://en.wikipedia.org/wiki/Sous_vide

Edit: I read a bit more on this, and was mistaken. Here is my original explanation: Basically a vacuum pump to lower boiling temperature; this puts a ceiling on achievable temperature for water-rich foods.

Actually, nowadays it looks like it's just slow cooking vacuum-sealed food in a temperature-controlled water bath.

Even as someone who has a sous vide set up, and uses it a lot, I prefer the results of reverse searing for decent quality steaks.

I have a sous vide set up as well, and while I find that it works great for chicken and duck, I agree with you that sous vide does something weird to steak. It's something about the texture. I know Kenji has written a few articles about how meat changes over different sous vide cooking durations, but I also wonder if the length of time changes the way fat renders somehow. I don't think it's been well studied. Searching the internet reveals I'm not the only person who has noticed this, but some people do not notice it, so there's not really a consensus on what's going on.