"The blood shall be a sign for you on the houses where you live; and when I see the blood I will pass over you, and no plague will befall you to destroy you when I strike the land..."
Toughness (T) is a stat to represent your character's ability to withstand injury, disease and poison. Tougher characters take less damage from wounding attacks.
Five points in toughness increases your Damage Reduction by one damage per second. This is true for all the classes.