I think it has to be the best move, and a sacrfice for material
Brilliant Moves in New Game Analysis Report

This is my fourth, and the first one is my fifth. I don't want to go hunting for brilliant moves 1-3.

Alright never mind. I just played my 6th. That makes 2 tonight. Here it is. Let me now what you guys think about all 3. https://www.chess.com/analysis/game/live/44596226793?tab=review#:~:text=https%3A//www.chess.com/analysis/game/live/44596226793%3Ftab%3Dreview%26move%3D13%26tab%3Dreview%26classification%3Dbrilliant%26autorun%3Dtrue One of my best games with 80% accuracy. But this guy had a TON of blunders. He never stood a chance!

Brilliant moves outranks best moves.
Best moves are the moves found and assessed as best by the engine (whether you played it or not)
Hence brilliant moves are only made by the human player.
The engine assesses a move to be brilliant only after it is played (can never be proposed as mentioned above).
The engine was capable to assess a move to be brilliant in comparison to its best move when it is played by finding the outcome to be better than the engine proposed (its best move).
Hence a brilliant move is one that is proven to be best only if the engine had gone into a depth that is further than the depth it traverses, but it does not. This is why it can only figure it out after it is played by the human player.
Lol. Wrong.
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You guys are both wrong haha!
Here it is from the chess.com website:
"Brilliant (!!) moves and Great Moves are always the best or nearly best move in the position, but are also special in some way. We replaced the old Brilliant algorithm with a simpler definition: a Brilliant move is when you find a good piece sacrifice. There are some other conditions, like you should not be in a bad position after a Brilliant move and you should not be completely winning even if you had not found the move. Also, we are more generous in defining a piece sacrifice for newer players, compared with those who are higher rated.
Great Move is a new move classification that is denoted by a single exclam (!). These are moves that were critical to the outcome of the game, such as going from losing to equal, equal to winning, or finding the only good move in a position. Similar to Brilliant moves, we are more generous on what we call a Great Move for new players compared with high-rated players."
https://support.chess.com/article/2965-how-are-moves-classified-what-is-a-blunder-or-brilliant-and-etc

the difference between the best move and the brilliant move is the best move is the brilliant move is the best move but tricky to find
What makes a move tricky to find though? I just played this game: https://www.chess.com/analysis/game/live/56330630979?tab=review
Look at move 24 for white, it gives Nde4+ as brilliant, but if you replace it with Nge4+ which leads to the same checkmate, it is only classed as best move.
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