Natural 20
From Legends of Cphera
When a d20 roll produces a twenty, that twenty is said to be "natural" (i.e. It occurred naturally and hasn't been modified by any bonuses). This is as good a roll as you can get, and in some cases it gives special results, depending on the nature of the check.
Attack Rolls
A natural 20 is always a critical threat. You automatically hit and you may get a critical hit.
Skill, Ability Checks, and Magic
A natural 20 qualifies only as a roll of 20. If a roll of 20 is not good enough to succeed at the task in question, you do not succeed.
Saves
A natural 20 represents automatic success on a save.
