On this website, a "great" move is the only move that wins, draws (in a bad position), or otherwise doesn't immediately lose (in a winning/drawn position), draw (in a winning position), or simply worsen your position. Calling it a "critical" move is more accurate.
Um.... 10 Great moves in a horrid game. Is it even impressive
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https://www.chess.com/analysis/game/live/140536348142/review?move=171 What the heck, absolute twister of horrid moves