In the Bible, the word we have as “church” is an assembly or group. Who is gathered together, and why? By inference, the church assembly is a gathering of Christians, beleivers in the person, work, and teachings of Jesus Christ. By instruction, they are gathered to encourage, admonish, and exhort [ed.] one another.
Now this could hardly be a perfect definition, but I deliberately avoid including therein some church-related things on which I might opine; sacraments, leadership, doctrine, etc. The Lord’s Supper and Baptism and several other issues are important, and intelligible, but not, I think, essential to church as described in the New Testament. I think that I understand what the Bible teaches about these matters, but if I come to joining a church, the question will not be, “Do they have the right Lord’s Supper?” or “Do they have correct baptism?” The question will be instead, “Are these believers gathering to encourage, admonish, and teach one another?”