Charisma

Charisma is part of the main stats, also called SPECIAL-Co values.

In these rules it's usually abbreviated with a single "C". Do not confuse it with Courage, which is abbreviated with "Co".

A combination of looks and charm. Influences among other things, how people around you react on your character, their ability to influence humans (and similar) and to conduct trade.
Charisma is therefore the most important stat.