We use secular to refer to that part of our society that is not religious. We also talk about the non-religious people as being part of a secular society.
I want to raise a warning flag. I doubt that we really have much of a secular society.
What we have today is a large part of America that believes religion can and does play a meaningful role in our polity. This is both the traditional civil religion that uses God carefully in our political life, and the enthusiastic religion that expects our leaders to be religious people.
What I want to raise a flag about is the perception that there is a secular opposition arrayed against the 'religion in public life' platform that most of America has signed-off on.
Many observers would locate that secular opposition in the body of urban atheists along with a few traditionalists who have 'separate church-state' ideologies from a by-gone era.
My problem is that I don't think there are many urban atheists except in survey data. I would guess that among the 20% who say that they don't believe in a god and the next 20% who have only a nominal religious affiliation that close to half are Lefty Fundamentalists and fellow travelers for whom Leftism is a full blown religion.
I listened to Sam Harris one evening talking to a San Francisco audience in rapture to hear God and religion attacked. But nearly the entire audience were Lefty Fundamentalists for whom Armageddon is just around the corner with global warming and the satanic behavior of global big business is destroying the planet and exploiting the poor.
Sorry, I doubt there really is much of a truly secular class in America....or Europe for that matter. People who are mistaken as secular are just as religious as the rest, except that their religion is Lefty Fundamentalism.