What is the difference between a brilliant move and the best move?

Question

As far as I know, nowadays the chess engines can judge that a move is the best or that it is brilliant (usually denoted by ! or !!). I was wondering what is the precise criterion for this classification.

I was reading some forums and stepped on this discussion. There, some people claim that a brilliant move is one that the engine does not find and, a posteriori, finds it to be brilliant. Some other people claim that a move is marked as brilliant only if the player continues the game responding with the absolute best moves, for some number of moves ahead. Finally, there is also the opinion that a brilliant move simply cannot be reached by the engine up to a certain depth, which is what I would instinctively think too. Thus, this would imply that if the engine performed a sufficiently large-depth analysis then there would not any be brilliant move markers. Is this correct?

Finally, my question: What is (if it even exists) the specific criterion, based on which a chess engine marks ones move as brilliant, rather than simply the best.

Answer 1

Just my opinion.

The best move is the one with the best evaluation, with the exception of the "computer moves" which only delay the real threat for a move.

A brilliant move is not only good but has a surprise value. A correct sacrifice easily qualifies, but a move with an unusual (and correct plan do tend to be brilliant. There are two examples: a computer played Re1 in it's match against Kramnik with the plan to get the rook to g3 and a game (I think) by Fischer where he played a4 followed by Ra1-a3-b3 just to make black slightly more passive by having to defend the b6 pawn. (Normally every contributor would try to find these examples, but. right now, I don't have the energy.)

BTW, this question is really a matter of opinion and shouldn't be asked. When/If this question gets closed, try to learn from the experience.