The term church was first used by Christ during the time when he declared that He will build the church as it was written on the book of Matthew 16:18. Definitely, the Apostles who heard it from Christ knew what it means, because they didn't questioned Christ about it.
However, Christians today although used this term (church) have different understanding on what the term Church means. Some said, it is a building used in Christian worship and the others said it is a religion or a group of believers.
And for us to make sure what the term "Church" means, we need to ask the Bible and let it answer our questions.
Our first question is: What is church? According to the Apostle Paul, the church is a body of Christ.
18 And He is the head of the body, the church, who is the beginning, the firstborn from the dead, that in all things He may have the preeminence. (Colossians 1:18, NKJV)
If the church is the body of Christ, is it the physical body of Christ? Apostle Paul said that the members of the church or the body are men.
5 so we, being many, are one body in Christ, and individually members of one another. (Romans 12:5, ibid)
In other words, the church is not the physical body of Christ and its members are not the physical body-parts but men. It is the body of Christ in which Apostle Paul, the other Apostles and their brethren are parts of it.
To make it clear, let us ask the bible: Is the body made up of one part? Apostle Paul's answer is clear. The body is not made up of one part but many.
14Now the body is not made up of one part but of many. (I Corinthians 12:14, NIV)
These parts are joined and knit together by joints.
16 from whom the whole body, joined and knit together by what every joint supplies, according to the effective working by which every part does its share, causes growth of the body for the edifying of itself in love. (Ephesians 4:16, NKJV)
Thus, a body is an organization of body-parts. And since the church is also a body, in which its members are men, so the church is also an organization of men whose head is Christ.
We should not forget this, that according to the Bible, the church is not a building but an organization.