Ability Scores

Abilities generally describe a creature's physical and mental characteristics, and determine the creature's strengths and weaknesses. Ability modifiers, based on the ability scores, contribute to all kinds of effects like attack rolls, defenses, and skill checks.

Defenses

Your defenses are your ability to protect yourself against various types of attacks, such as a goblin swinging a sword at you or a wizard casting fireball. Different defenses will protect you from different attacks.