The "technical" term for what you describe is blundering. The winner amongst two humans playing each other is mostly defined by who blunders first. Some of these are sometimes so obvious that we have a take-back rule amongst friends for obvious giveaways. Mind you, its not "can I take this move back", its "you want to make another move, this one is too stupid"
What they are describing is that feeling you get when you suddenly realize you are losing even though you are even in pieces, because you suddenly see your opposition has superior positioning and board control
It's not a blunder, because there wasn't one particular move where the game slipped away.
The "oh shit" move doesn't necessarily make your position suddenly way worse, it can be just the moment when you realize how much better your opponents position has been for a while.
Hence why I talked about the feeling you get when you realise you have mis-evaluated rather than trying to define it precisely.
From the OP:
> But when AlphaZero plays, and you watch Stockfish's score, the reason it wins is that it makes moves Stockfish thinks is poor, so it rates AlphaZero's moves poorly, and then all of a sudden it has an oh shit! moment when it realises that AlphaZero is actually ahead, and its score jumps. It's really a look inside the computer's head while it's being beaten by a better player.
If you watch from here in game one you can see the "oh shit" moment, as Stockfish's evaluation drops from +1 to even to -1: https://youtu.be/Q5EPqM8gS7k?t=255
There were blunders in the first round of games. I remember this vividly because I went through all the games with the exact same version of Stockfish with the same time controls and it thought some of its own moves were blunders. This is partly why people were so puzzled by the setup that led to this.
A blunder is when someone makes a wrong move then and there that costs them the game. At AI levels, there are very few, if any, blunders. I think parent commenter means a strategic mistake, where they made a mistake about 5 moves in advance.
True. The technical definition of a blunder on lichess and chess.com is that it puts you in a losing position. You can blunder further while in the losing position. And your opponent can blunder which puts them in the losing position, only to be reversed by your blunder.
A mistake is like a blunder but you're still winning, but it could be a blunder in a worse position. An inaccuracy is a bad move that doesn't cost you.
At least on lichess, the blunder/mistake/inaccuracy distinction is based only on how much the evaluation moves. Going from +10 to +6 is still a blunder.
