Courtesy Padding is one of two types of padding on a weapon. As opposed to Striking Surface, courtesy padding is not a strike-legal section of the weapon.
The padding is applied to prevent accidental injury on the battlefield. Courtesy padding can be used on swung weapons (such as a flail, axe, mace, spear, or glaive) in place of striking surface. The purpose of this padding is to protect from accidental contact, and is not a valid striking surface. Depending on the thickness and firmness of the padding, sometimes more than one layer of foam will be need. When checked the weapon's core should not be able to be felt by a checker (if core can be felt, this will cause a weapon to fail).
Courtesy padding near the striking surface of a swung weapon should often have nearly as much padding as a striking surface (especially in the case of flails, and weapons with minimum striking surfaces).
From the Book of War:
1.3.2 All non-striking surfaces must be padded adequately to prevent personal injury from incidental contact.
See also: Basics of Weapon Checking