Direttamente sul manuale del giocatore dove viene descritto il Carisma

Charisma measures a character’s force of personality, persuasiveness, personal magnetism, ability to lead, and physical attractiveness. This ability represents actual strength of personality, not merely how one is perceived by others in a social setting. Charisma is most important for paladins, sorcerers, and bards. It is also important for clerics, since it affects their ability to turn undead. Every creature has a Charisma score.

Aggiungo come nota che l'SRD è tratta dai manuali "core" ovvero PH, DMG e MM1.