Persona is a character's ability to integrate with other people, to charm, convince, romance, interrogate, befriend... if it involves dealing with other people, this is the stat to look to.
A person with a Persona of 10 may have some kind of social disability.
A person with a Persona of 30 would be an introvert, not very popular, and otherwise socially awkward.
A Persona of 45 is average.
If someone were to have a Persona of 60, that person would be extroverted and well-adapted to life within social circles.
If someone had a Persona of 80, they would most likely be a social butterfly, and would also be very skill at adapting to changing social climates and even being the catalyst of that change.
A Persona of 100 would indicate a social genius, someone who should be working for the CIA... or possibly even running it.