A sacrifice in chess is a move in which a player deliberately gives up material — a pawn, a minor piece (knight or bishop), or a major piece (rook or queen) — in exchange for a different type of advantage: a decisive attack, a tempo gain, or a structurally superior position.
Unlike a simple blunder, a sacrifice is intentional and calculated. There are two main categories: the tactical sacrifice, where the compensation is concrete and forced (checkmate in a few moves, or recovering the material with interest), and the positional sacrifice, where the compensation is more subtle — better piece coordination, a weakened enemy king, or a lasting initiative. At the 800–1400 ELO level, the vast majority of sacrifices worth mastering are tactical in nature.
In practice, before committing to a sacrifice, ask yourself two questions: "What does my opponent gain concretely?" and "What do I get in return?" If you cannot answer the second question precisely by calculating at least two or three moves ahead, it is better to hold back. An uncalculated sacrifice is simply a loss of material.