what is a Blunder??

In chess, a blunder is a very bad move. It is usually caused by some tactical oversight, whether from time trouble, overconfidence or carelessness. While blunders are more common in amateur games, all players make them even at world championship level. While a blunder may seem like a stroke of luck, giving the opponent opportunities to blunder is an important skill in over the board chess.

What qualifies as a "blunder" rather than a normal mistake is somewhat subjective. A weak move from a novice player might be explained by the player's lack of skill, while the same move from a master might be called a blunder. In chess anotation, blunders are typically marked with a double question mark, "??", after the move.

Especially among amateur and novice players, blunders often occur because of a faulty thought process where they do not consider the opponent's forcing moves. In particular, checks, captures, and threats need to be considered at each move. Neglecting these possibilities leaves a player vulnerable to simple tactical errors.