Increases the amount of damage you can block with a shield.

Strength does not affect critical hit chances at all. Strength does not improve your chance to block, but rather the amount blocked when you succeed. This amount is determined in part by Strength (and the other part by your shield).

Agility (AGI)
Increases your attack power with ranged weapons.

Increases your armor.

Increases your chance to score a critical hit with a weapon.

Increases your chance to dodge attacks.

Rogues gain a much stronger bonus to dodge from agility than other classes.

Hunter & Rogue: Increases your attack power with melee weapons.

Stamina (STA)
Increases Health points.

Intellect (INT)
Increases the rate at which you learn weapon skills.

Increases your Mana points.

Increases your chance to score a critical hit with spells.

Spirit (SPT)
Increases health and mana regeneration. Spirit affects all characters' mana and hit point regeneration rates in and out of combat.

Weapons
Attack (AR) - Attack Rating.
Power (AP) - Attack Power.
Damage (DMG) - Weapon Damage.

Armor
Defense (AC) - Defense Rating.
Armor - Physical Damage Reduction.