Melee special attack

A melee special attack is the swing used to initate a variety of single-target combat feats, which all can cause a special penalty, in addition to normal weapon damage. Related feats are Trip, Sunder, Stunning Blow, Slicing Blow, Hamstring, and Sap. (Improved Feint is not a special attack, because it cannot do normal damage)

Such an attack is activated by using the icon for the particular feat. A single swing animation is made at your standard BAB, during which you cannot be moving (this can be a significant penalty, as you possibly can't catch a running monster). If it hits, the feat may apply additional penalties beyond just damage. After a melee special attack, there is a delay before you can attack again, meaning that using special attacks will decrease your overall attack rate. Essentially, you must wait for the entire remainder of the "combat round" before attacking again.