A Critical Hit is a modifier on an Attack that makes it do more damage than normal. There are often some form of particle effects, or other method of conveyance communicating to the player that a Critical Hit was achieved.
Critical Hits may be attached to a random chance, and when they are, that chance may be dependent on stats. Random-chance Critical Hits may be more likely under certain circumstances, and may sometimes even be made guaranteed via Status Effects. In other cases, a Critical Hit may be completely predictable and done by fulfilling specific requirements before or during the attack. Weakspot Attacks are a type of Critical Hit that are typically nonrandom.