Shield parry is a Warrior skill that can be practiced to increase the Parry bonus (PB) gained from equipping a Shield. The PB gain, before weight effects and rounding, is a function of the character's Dex, prac%, mood, and the shield's PB value.
In Game Description
Warrior skill: Shield parry allows one to attempt to turn aside attacks with their shield, rather than body armor (or worse, not at all). The extent to which one is able to defend themselves depends on the skill, and vitally upon the fact that they are using a shield as well, as it is impossible to block an attack with a shield if the defender has none.
-  - WoTMUD Archives forum posting on Encumbrance testing
-  - WoTMUD Archives forum posting on OB/DB/PB testing