Defense & Toughness

From Introduction:

Some characters have a better ability to weave and dodge attacks than others, ingrained through years of training or experience. This is represented mechanically by the character's Defense TN. It replaces the normal target number (TN) to hit a character, as well as the usual rule of increasing the severity of damage for every magnitude of success on the attack.

A character's Defense TN is actually two numbers, one representing the target number to hit the character and the other representing the target number to hit the character and stage up the severity of the damage. This score is written with a slash separating the two numbers.