in the hexaco model of personality traits, to what does the “x” refer?

In the HEXACO model, the letter “X” stands for Extraversion. This dimension captures traits related to social engagement, assertiveness, energy in social interactions, and sociability. It is one of the six core factors in HEXACO, alongside Honesty-Humility (H), Emotionality (E), Agreeableness (A), Conscientiousness (C), and Openness to Experience (O).