Melee Damage types:
 Thrust
 Crushing
 Cutting
 Chopping

Melee Defense types:
 Thrust
 Crushing
 Cutting
 Chopping

 Lets look at how these show up on paper. Here we have a Longsword, notice its base attacks. Depending on the attack you choose to do, will determin the damage. Example.

Longsword:
 Cutting: 15
 Thrusting: 16
[choosing to do a thrust will give you different damage than choosing to do a cut, and vice Versa]

Now, lets take a look at armour. Someone is wearing maille armour along with a padded jacket underneath. This combination would give defenses which would look like this.

Padded jacket:
Cutting defence: 3
Thrusting defense: 3

Maille armour:
Cutting defence: 13
Thrusting Defense: 9

Combined defenses:
 Cutting defence:16
Thrusting defense: 12
  [With these defenses, it would make sense that you'd want to thrust against this opponent]
 There are other reasons one may want to thrust, or cut over the other defences. Take this halberd