Abbreviated CH
Charisma is the catch-all term for aggregated social ability. Someone with above average CH does well in social situations, while someone with below average CH does not.
It is not necessarily related to physical attractiveness, though that certainly plays a role. Neither is it necessarily related to introversion or extroversion. Those tendencies also play a role, but are not the deciding factor.
Charisma is the primary ability for social tasks, and the default Stat for reaction checks.