People commonly refer to a church building as a church, but this is not really the church. The church is people, all the followers of Christ together. The New Testament uses several metaphors for the church-the body of Christ, a holy temple, a spiritual house, household of faith, people of God-but the church is the corporate body of Christians.
You can speak of the church as a local assembly of believers or the totality of believers in a city, a country, or around the world. You can even speak of the church throughout the ages as all the believers who have ever lived. However you speak of it, the church is the people of God.