Here are definitions of various rules. Ability Check An ability check is a D20 Test that represents using one of the six abilities—or a specific skill associated with an ability—to overcome a challenge. See also “Playing the Game” (“D20 Tests” and “Proficiency”). Ability Score and Modifier A creature has six ability scores—Strength, Dexterity, Constitution, Intelligence, Wisdom, and Charisma—each of which has a corresponding modifier. Add the modifier when you make a D20 Test with the corresponding ability or when a rule asks you to do so. See also “Playing the Game” (“The Six Abilities”).