Melee combat is resolved using a chart of possible results for each attack. The sequence of results is: auto-crit (a target not standing up is always critically hit, and this value is either 0% or 100% for each attack), miss, dodge, parry, glancing blow (players versus monsters only), block, critical hit, crushing blow (monsters versus players only), and finally a normal hit. If the percentage chances add up to more than 100% then latter results will not be performed at the expected % rate because the random roll used to get a result from the chart is from only 1 to 100.
Ways of avoiding damage are miss, dodge, evade, parry, block, absorb, resist, immune, and reflect. There's also an hypothetical deflect outcome about which we need more information.
Miss
Only applicable to physical damage. Any physical attack, assuming that both attacker and attacked are the same level and have no modifiers to their hit rate, has a 5% chance to miss.
Dodge
Only applicable to melee attacks. Your chance to dodge is increased by agility and defense.
Parry
Only applicable to melee attacks. Your chance to parry is increased by defense. Only certain classes are capable of learning how to parry attacks, and only attacks from your front may be parried.
Evade
Applicable to any type of damage, or even non-damaging debuff. A mob that is in a position where the game believes players are using an exploit to avoid being damaged will go into Evade mode at which point it is effectively immune to all attacks.
Absorb
Applicable to any type of damage. This is usually the result of having a buff such as Power Word: Shield, which absorbs a limited amount of damage before failing. Certain shields can only absorb certain kinds of damage, so read the description before wondering why you're still getting hurt.
Resist
Only applicable to magical damage. This is basically the magical version of a miss. Your chance to resist a spell or other effect is based on your resist of that element, as well as your level. You can also partially resist some spells, taking only 25%, 50%, or 75% of the normal damage.
Immune
Applicable to any type of damage. This is the result of a mob having a coded ability to be immune to certain attacks (i.e. Scorpid Sting does not work on most bosses) or a player using some skill or item to protect them from damage (i.e. a Paladin's Blessing of Protection). These are either permanent (mob immunity) or time-limited (Paladin blessing) and will not fail regardless of how much damage you throw at it.
Reflect
Applicable on non-AoE spells only. A Reflected spell will bounce back to its caster, acting as if it was cast on him. A Reflect can be caused by a buff such as improved mage's Frost Ward or Fire Ward, a Warrior's Spell Reflection, Destructive Skyfire Diamond's proc, or certain mobs' innate abilities.
Deflect
This is an outcome which has been found by looking to GlobalStrings and CombatFeedback lua files, in Blizzard's UI (FrameXML), which might be added later by Blizzard to possible results for auto-attacks and physical abilities.
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