Tempo

In chess, a tempo is a 'move' considered as a unit of time; to 'gain a tempo' means to make progress (development, attack, improving a piece) while forcing the opponent to respond, effectively getting a move for free, while to 'lose a tempo' means wasting a move that does not contribute to one's plan, such as moving the same piece twice without purpose. Tempo matters strategically because chess is a race to develop pieces, control the center, and generate threats before the opponent does, so every move not spent efficiently gives the opponent a chance to catch up or seize the initiative. A common example is attacking an opponent's piece with a developing move, such as playing a knight to a square where it both develops and threatens a bishop, forcing the opponent to spend a move retreating it rather than developing their own position. Gaining multiple tempi in the opening or middlegame often translates into a lasting initiative, faster attack, or material gain, which is why openings are often evaluated partly by how efficiently they develop pieces without wasted moves.