Sacrifices range from small (a pawn sacrifice, or gambit, to gain a lead in development or open a file) to spectacular (a queen sacrifice that forces checkmate a few moves later). What separates a sacrifice from a blunder is intent and compensation: the sacrificing side has calculated, or at least judged, that the resulting attack, structure, or activity outweighs the material given up.
Common sacrificial patterns include the Greek gift (Bxh7+ to expose a castled king), exchange sacrifices (giving up a rook for a minor piece to gain a strong outpost or ruin the opponent's structure), and clearance sacrifices (giving up material simply to vacate a square or line for another piece). Recognizing these patterns lets a player sacrifice with confidence rather than guesswork.
Not every sacrifice needs to be immediately "correct" in an engine sense — many practical sacrifices succeed because they create problems the opponent must solve accurately, often under time pressure, even if a computer could in principle find a perfect defense.