Ability score

In the Dungeons & Dragons role-playing game, game mechanics and die rolls determine much of what happens. These mechanics include:

All player characters have six basic statistics:

An ability score is a natural number, with a value of 10 or 11 representing average human ability.

Additional:

Beginning with the 3rd Edition, each score has a corresponding ability modifier, where Modifier = (Score − 10)/2, rounded down. This modifier is added to the appropriate dice rolls. For example, the strength modifier would be added to the damage dealt by a sword, the dexterity modifier to Armor Class (see below) as the character's ability to dodge attacks, and the charisma modifier to an attempt to smooth-talk a merchant.

There are several methods of determining a character’s initial ability scores during character creation:

Armor class (AC) is a rating used to determine how difficult it is to damage a creature/character. It is based on several factors such as a creature's natural aversion to physical injury, magical enhancements, and any protective garments worn. The dexterity ability score grants bonuses to AC.

In 4th edition, there are three defenses that function similarly to armor class. Fortitude is based on strength or constitution; it represents a character's endurance to pain. Reflex is based on dexterity or intelligence and can be modified by a shield; it represents a character's ability to dodge. Will is based on wisdom or charisma; it represents a character's strength of mind and resistance to mental attack. These defenses are typically lower than AC, so an attack against fortitude is usually better than an attack against AC.

Hit points (HP) are a measure of a character's vitality or health; they are determined by the character's class (certain occupations breed hardier people) or race, and Constitution score. Hit points are reduced whenever a character takes damage.

In the original D&D game a character died when his/her hit point total reached 0. First edition AD&D introduced an optional rule in which a character died when his/her hit points reached -10, with beings falling unconscious at 0 HP, and creatures reduced to negative HPs continue to lose HPs due to bleeding, etc. unless they are stabilized by aid or healing (natural or magical). In third edition, this rule became part of the core rules.

...
Wikipedia