This is the base chance to cause a critical hit in combat. Characters with high combat skills, or high quality weapons, will also score more critical hits. The difference between a successful combat roll and the proper weapon skill is modified by a formula and added to the Critical Chance stat. Then another roll is made, and if it is under the modified Critical Chance, a critical hit is scored. And that is a completely different table that depends on the type of critter you are attacking, and where you hit them.