Dodge

Any character can dodge an attack, causing it to miss. You can increase your chance to dodge by increasing your agility stat, and by using armor or items that give flee or evasion rating.

In addition, targets that are substantially higher level than their attacker are more likely to dodge the attack.

Dodge reduction

Characters that have more than two monsters attacking them at the same time, have their chance to dodge an attack reduced. For example, even if you can dodge a level 20 monster with a 95% chance at level 30, if you have ten monsters meleeing you, your chance to dodge them will be much lower, and they will be much more likely to hit you. This doesn't necessarily mean they will crit; most of the attacks that land will still be regular hits.