In the Dungeons & Dragons role-playing game, game mechanics and die rolls determine a lot of what happens.

Ability score

---

All characters have six basic statistics:

• Strength (STR) determines brute strength, carrying capacity, and melee ability.
• Dexterity (DEX) determines agility and coordination.
• Constitution (CON) determines hit points and physical resistance.
• Intelligence (INT) determines a character's ability to think logically.
• Wisdom (WIS) determines awaress of surroundings and intuition.
• Charisma (CHA) determines force of personality and interactions.

An ability score is a number with a modifier (mod) associated with it; -1 for every number below ten, +1 for ever two numbers, rounding down, above ten. So, for example, an ability score of eight, two lower than ten, would mean a modifier of -2, while an ability score of 17, 7 above ten (3.5*2; three and a half two's above 10: round down for 3*2 above ten) means a modifier of +3. This modifier is added to the appropriate dice rolls. For example, strength would be added to damage dealt by a sword, dexterity to Armor Class (see below) as the character's ability to dodge attacks, and charisma to an attempt to smooth-talk a merchant.

There are creatures without certain ability scores (Undead, for example, lack constitution), though that is not the same as having a score of zero.

There are several methods of determining a character's ability scores, including rolling, a set array of scores, and point buy.

Armor class

---

Armour class (AC) is a statistic use to determine how difficult it is to hit a creature/character.

• Armor - a number indicating the effectiveness of the armor worn by the character. Leather armor will give a smaller bonus to AC than full plate will. Armor can be enchanted to provide a greater bonus to AC.
• Shield - a number indicating the effectiveness of the character's shield. A light shield or buckler will give a smaller bonus to AC than a heavy shield will. Shields, also, can be enchanted to boost their AC bonus.
• Dex - Dexterity modifier (see ability modifiers, above). Indicates the character's ability to dodge attacks. If the character is wearing heavy armor that hampers their movement, they can only add a certain amount of their dexterity to their AC, because they are less able to dodge.
• Size - a number indicating how hard they are to hit because of their size. Bigger targets are easier to hit, and smaller targets are harder to hit; the smaller the character (in terms of size categories), the bigger a bonus they get to AC. The larger the character, the greater the penalty.
• Natural - a number indicating the effectiveness of the character's natural armor (hide, thick fur, scales), if any, at stopping attacks.
• Deflection - a number indicating the effectiveness of any number of effects, if any, that make attacks on the character veer off course.
• Misc - any bonuses or penalties to AC not covered in the other categories; includes spells and non-armor/shield magic items.

An attacker must roll higher than his opponent's AC to score a hit with a weapon/spell.

Touch AC: how difficult it is to touch the character with an attack. An attack may clank harmlessly off armor (not dealing damage) but still hit the defender; touch AC is a character's armor class, disregarding armor and shield bonuses (because armor and shields do not make coming into contact with the character any easier or more difficult).

Flat-Footed AC: how difficult it is to hit the character when they are surprised and unable to react to an attack (that is, unable to dodge). This is the character's AC, disregarding dexterity (because the character can't dodge).

Attacking

---

When a character makes an attack, a 20-sided die is rolled and a certain number is added to determine success/failure.

The number added to the die roll is actually several different modifiers combined, coming from different places. These modifiers include the character's proficiency with the specific weapon and weapons in general, the quality of the weapon (superior craftsmanship or magical enhancements), the modifier of the ability associated with the weapon (strength for melee, or close-quarters, weapons, and dexterity for ranged weapons), magical effects improving/hampering the character's ability to attack, and any special experience the character has fighting a certain foe. If the dice roll, plus all applicable modifiers, is higher than the defender's armor class (see above), then the attacker hits the defender and can proceed to the next step, determining damage.

If the attacker hits the defender, she proceeds to determining damage. A certain die is rolled, depending on the weapon being used; the more powerful the weapon, the more damage it is capable of doing, and the higher (more-sided) its damage die will be, for a higher possible damage roll. To this damage roll, modifiers are added, including strength bonus (melee weapons only), weapon quality, and magic affecting the attacker. The damage roll, plus all applicable modifiers, is deducted from the defender's hit points (see below).

Hit points

---

Hit points (HP) are a measure of a characters vitality or health; they are determined by the character's class (certain occupations breed hardier people) or race, and constitution score. Hitpoints are reduced whenever a character takes damage. When a character is reduced to 0 hit points, he drops to the floor, conscious but unable to act. When a character is reduced to negative hit points, he falls unconscious, and dies when his hit points drop to -10 or less.

In online communities, over IM, etc., hit points is often used as one word, hitpoints, for ease of typing; it's the same thing.