A bludgeoning attack is basically a speedy impact of a blunt object, such as a simple bash of the club. They are made by fists and weapons like maces, hammers and slings. Throwing non-weapons such as boots, beerbottles and food rations at somebody are also considered bludgeoning attacks, as is bashing your opponent with a bow or crossbow in melee.
Protection from bludgeoning reduces the damage received from such an attack.