Piercing is a damage type found in the Castlevania series. It involves taking a bladed item and thrusting it forward in a kind of jab instead of swinging with it, in an attempt to pierce through the defenses of an enemy.
Dawn of Sorrow and Harmony of Despair are the only games that distinguishes between Piercing and Slashing attacks. Any weapon that thrusts its sharp pointed tip into an enemy, deals piercing damage. This includes knives, rapiers, and spears. Guns can deal piercing damage too, since shooting is considered piercing.