Armor negating and penetrating?

[Coldshard]

Probably a silly question, but I havent had much luck in looking through the boards or the manual to get a definitive answer..

What exactly is negated and penetrated by these types of attacks? There are various levels of protection, defense, block, parry, and whatever else..

For penetrating whatever is affected by the above is instead only halved. Do fractions get rounded up or down for this check?