A bit out of date, as it still cites Defense as a stat, but:
Avoidance vs. mitigation
Defense, dodge and parry are called avoidance stats, as you avoid the entire effect of the attack. Block is called mitigation, as you mitigate (lessen the effect) of the attack. So for example if you have 20% dodge, 20% parry and 20% block, you have 40% chance to take no damage and 20% to block some of the damage.
I can verify that as long as I've been tanking (around 4-5 years now), Avoidance has been the set of stats that allow you to avoid an attack completely, while mitigation is the set of stats that allow you to reduce your incoming damage partially. Aggathon is correct.
Defensive Stance and Equivalents