post #4900865

A natural 20 (or sometimes called a "nat 20" for short) in d20-based systems refers to rolling a 20 on a 20-sided die. This typically gives a critical success on certain rolls, like attack rolls or saving throws. (The exact mechanics depend on the roll being made, the version being played, etc.) Outside of d20 systems, a nat 20 may simply refer to an instant or guaranteed hit/success.

The opposite is rolling a natural 1, or critical failure.

See also

• d20
• gameplay_mechanics