I am somewhat suspicious of the number of churches around here that claim 70-80% of their members are from the ranks of the "unchurched" population.
I associate "unchurched" with my African missions experience: never, ever been Christian.
Obviously, in the Bible-belt south there aren't many "unchurched" people unless they are recent immigrants (and virtually none of the Hispanic population is unchurched).
I think it is a point of pride and straining for legitimacy for a church to claim such a high number of "unchurched" people in its ranks. They are fending off the accusation that their new mega-church edifice is just rearranging the sheep - taking them from more traditional congregations and entertaining them with a more appealing show.
Here's Barna's definition:
An adult (18 or older) who has not attended a Christian church service within the past six months, not including a holiday service (such as Easter or Christmas) or a special event at a church (such as a wedding or funeral).
Thom Rainer has a more stringent definition: one who has not been in church, except sporadically, for at least ten years (most for a lifetime).
A Presbyterian group says: The general definition of an unchurched person is anyone who has not attended church other than Christmas, Easter or special events in the past five years.
My guess is that some are sliding towards definitions even less stringent than Barna - saying something like "someone who was uninvolved in his or her previous congregation," "was just an attender," or "never was a regular weekly church-goer". Barna says if you miss 24 Sundays (excepting high holy days) and you are a prime unchurched prospect. I guess that means anyone can woo you into their group with a clear conscience. No sheep rustling here!
I wonder if the reason "unchurched" has become a popular term is that it would be much harder to say these people aren't Christian. But because we want it to sound like we aren't simply taking sheep from other flocks, we declare people "unchurched" so it sounds like we are carrying the Gospel to places its never been.
Most of us in our congregation weren't unchurched people. We can't even approach the high percentages of unchurched "members" of the congregations around us. Maybe I would say that 10% were not churched. The few I would point to as being unchurched before joining with us in a faith community hadn't been in a church, nor practicing a person faith-walk with Jesus, in over 20 years, if ever. Such a person I would say was "someone coming to Jesus."