Most people think of the church as a building or an institution. However, the Bible uses a unique metaphor to describe the Church it describes the church as the bride of Jesus Christ.
Wives, submit yourselves to your own husbands as you do to the Lord. For the husband is the head of the wife as Christ is the head of the church, his body, of which he is the Savior. - Ephesians 5:22-23
This video by Central Christian Church in Las Vegas answers the question What is the Church?