AC

AC is your avoidance class, it is defined roughly as follows:

  10 Very easy to hit
   0 Fairly hard to hit
 -10 Very hard to hit

Any AC above 10 is evaluated as 10, and any AC below -10 is evaluated as -10.

AC is your chance of AVOIDING being hit, it does not directly lessen the amount of damage that you take upon being hit. If you are actually hit, then your armor's STOPPING value comes into play. The AC value used to determine whether or not you are hit is the sum of your ALL-AC (any AC that affects your whole body) and the AC given by the item(s) worn on the area of your body that was attacked.

NOTE: AC is NOT "armour class" but "avoidance class" !!!