ANSWER: The Greek word commonly translated church in the New Testament is ekklesia (Strong's Concordance #H1577). An ekklesia is not a building where believers gather to worship, as is commonly thought of today. The correct definition, based on its use in the Bible, is that it is a COLLECTION or assembly of those who have the spirit of God dwelling in them.
The word 'church' used in the Bible additionally can mean more than one assembly of believers meeting together. It can refer to ALL true Christians living in the world or even to the collection of all converted believers who ever existed in history. Jesus said the ekklesia or assembly he was to build would be founded on himself (and not on any man like Peter).
18 And so I (Jesus Christ) tell you, Peter: you are a rock (a small pebble), and on this rock foundation (the understanding of Jesus being the Messiah) I will build my church (Matthew 16:18)
The New Testament lists several locations where an assembly of believers met in homes to study the Bible and worship God. In Jerusalem, they met at the house of Mary and other unnamed homes (Acts 2, 5, 8). They met at Philip the Evangelist's house in Caesarea (Acts 21).
Christians met in Ephesus at the house of Priscilla and Aquila (1Corinthians 16, Acts 20). Believers also met in a least four separate homes in the city of Corinth (Acts 18, 1Corinthians 1, 16).
Christians met in at least six different homes in Rome (Acts 28, Romans 16). The house of Philemon hosted a weekly assembly in Colossae (Philemon 1). A group met at the house of Nympha in or near Laodicea (Colossians 4). The house of Jason in Thessalonica had weekly services (Acts 17). A group of believers met in a home in Troas (Acts 20). The New Testament refers to at least 21 distinct homes where first century Christians gathered to strengthen each other in the faith
What is the church? It is all those who have the Spirit of God dwelling in them. It is a spiritual organism whose names, written in heaven, are listed in the Lamb's book of life.
12. And I saw the dead, small and great, standing before God; and the books were opened; and another book was opened, which is the book of life. And the dead were judged out of the things written in the books, according to their works (Revelation 20:12).