I'm asking more about why a specific move is called a blunder. If you're playing as black, and white uses the Fried Liver attack, when you use the Bishop and do Bxf2+, Stockfish on Chess.com says that's a blunder. I'm curious as to why. I know it's (probably) giving up a valuable bishop, but White's King playing Kxf2 allows for Qh4 (thus removing the Queen from the threat of the rook on f7), and also possibly puts pressure on white's Bishop on c4.
Is it a blunder solely because there's no equal or greater exchange? Is it something else?