(I'm not saying this picture is accurate, just that it shows some of the various groups that would call themselves "The Church")
After reading Horton's post linked below, I thought again of the profit that comes from being refreshed about the nature of "The Church". The Westminster Confession of Faith does a tremendous job capturing the bible's teaching on this important question in the 25th Chapter-
CHAP. XXV. - Of the Church.
1. The catholic or universal Church, which is invisible, consists of the whole number of the elect, that have been, are, or shall be gathered into one, under Christ the Head thereof; and is the spouse, the body, the fullness of Him that filleth all in all.
2. The visible Church, which is also catholic or universal under the Gospel (not confined to one nation, as before under the law), consists of all those throughout the world that profess the true religion; and of their children: and is the kingdom of the Lord Jesus Christ, the house and family of God, out of which there is no ordinary possibility of salvation.
3. Unto this catholic visible Church Christ hath given the ministry, oracles, and ordinances of God, for the gathering and perfecting of the saints, in this life, to the end of the world: and doth, by His own presence and Spirit, according to His promise, make them effectual thereunto.
4. This catholic Church hath been sometimes more, sometimes less visible. And particular Churches, which are members thereof, are more or less pure, according as the doctrine of the Gospel is taught and embraced, ordinances administered, and public worship performed more or less purely in them.
5. The purest Churches under heaven are subject both to mixture and error; and some have so degenerated as to become no Churches of Christ, but synagogues of Satan. Nevertheless, there shall be always a Church on earth to worship God according to His will.
6. There is no other head of the Church but the Lord Jesus Christ. Nor can the Pope of Rome, in any sense, be head thereof.