Wow, that's really weird!
Brilliant move worse than best move?!?!

Isn't the description of a brilliant move 'The best move, and tricky to find too!'?
Well, obviously it isn't.
Instead, it is "A sacrifice that is not necessarily the best move, but not very bad either".

"A move is brilliant if the engine doesn't think the move is best before the move is played at a certain depth. But after it is played when the engine analyzes the next move at the same depth, it'll figure out in hindsight that the previous move was better." according to Chess.com

"A move is brilliant if the engine doesn't think the move is best before the move is played at a certain depth. But after it is played when the engine analyzes the next move at the same depth, it'll figure out in hindsight that the previous move was better." according to Chess.com
That sounds very suspicious. What is your source?

Oh Magipi you were correct, I hadn't done enough research and it turned out that the definition I posted was only a popular opinion on Chess.com forums. Chess.com however defines it as what you defined it as, and I trust Chess.com the most.

Isn't the description of a brilliant move 'The best move, and tricky to find too!'?
Well, obviously it isn't.
Instead, it is "A sacrifice that is not necessarily the best move, but not very bad either".
my source was chess.com's description when u hover over 'brilliant' on the analysis page
where does that definition come from?

my source was chess.com's description when u hover over 'brilliant' on the analysis page
Wait, that can't be right. The Analysis page does not use words to describe moves. Are you talking about "Game review"?

A best move is the computers top pick, and would also be classified as a brilliant move. It the best move (engine move) was hard to find, and trick to find. By Chess.com's definition of a brilliant move.
It is the same of a great move. It would be the engines top pick, and changed the balance of the game.
So best moves means - The chess engines top choice in that positions.
A Great move means - The chess engines top choice, but changed the outcome of the game.
A Brilliant move means - The chess engines top choice, but the move was hard, and tricky to find.
Literally none of this is true.

This is a brilliant move, but d4 is apparently best.
At which depth of which engine is d4 the best move? Stockfish seems to prefer Nxe5 at all depths, even after minutes of calculating.

Well, I mean, best by definition means better than anything else.
I always assumed a brilliant move is a move that looks innocuous or even like a blunder but actually confers some kind of major advantage. It doesn't necessarily have to be the best move in order to fit these conditions.
I was analysing a game that I played (a daily one from the 2023 Daily Chess Championship) in which my opponent timed out (post-game analysis of course). In this game, the engine said that my opponent played a brilliant move (Ra1) but for some reason it said this wasn't the best move, which was f5
How can a brilliant move not be the best move? Isn't the description of a brilliant move 'The best move, and tricky to find too!'?