Secret Society 

The name would indicate a society, or group of individuals, that keep their existence secret from the masses, or at least from the established religions or governments.

If a secret society does a good job of being 'secret', then the rest of the world would not even know that they existed.  One the existence of a secret society becomes known, they cease to be secret.

Many people have accused the Freemasons as being a secret societyIs Freemasonry a Secret Society?

If the Freemasons are attempting to be a secret society, they have totally failed in that goal.

Why are secret societies formed?