Page 9 of the Game Manual
http://www.moddb.com/mods/vtm-the-final-nights/downloads/official-tfn-14-game-manual
You really should read this, but I'll be nice and let you be lazy and post it here.
Name: Defense
Description: Measures your character's ability to avoid taking damage of all types
in combat. The Wits attribute and the Dodge ability both contribute to the Defense
feat.
Dependencies: Wits and Dodge
Information: Often an overlooked feat because the effects aren’t immediately
apparent, but the Defense feat is your first line of protection when an enemy
successfully hits your character. When your opponent attacks, their damage is
calculated against your Defense feat and each point in Defense has a 50% chance
of reducing each point in lethality. The total damage is calculated and then your
soak feat subtracts the rest. Whatever is left over is the damage you take. Have you
ever punched an enemy but did 0 damage? That’s because their Defense feat was
much greater than your total lethality minus the skill requirement. Certain weapons
like the knife can also grant your character a bonus to Defense when wielding the
weapon.
. Thank you for the answer 
(and the patience)