I think that there are a lot of Christians out there who get baffled by this question. Not just Christians, but people in general. Many would answer something along the lines of, “Big building, stained glass windows, pipe organ”. Others would say something along the lines of, “Where two or more are gathered in His name…”, but that begs the question of if a couple guys are hanging out at and having a spiritual discussion, are they a ‘church’? Then there is the theological answer: “Where the word of God is rightly preached, and the ordinances (sacraments: marriage, baptism, communion…) are rightly practiced”.

I tend to go with the theological answer, but I would use scripture to describe it: They devoted themselves to the apostles’ teaching and to the fellowship, to the breaking of bread and to prayer. (Acts 2:42).

They devoted themselves to the apostles’ teaching: Word rightly preached.
They devoted themselves to the fellowship: Loving each other.
They devoted themselves to the breaking of bread: Communion (Sacraments).
They devoted themselves to prayer: Lifting each other up and worship.

Church is not defined by a building, but by people. It’s not a Sunday morning event, but a lifestyle. If more ‘churches’ would recognize this, then maybe more non-Christians would be drawn to Christ.