Historically, the attributes of what defines the church is found in the Nicene Creed:
1) The church is one - Christ died to save one bride, so there are not two, or three, or ten churches, but there is one church, and the members of that one church recognize it's fundamental unity.
2) the church is holy. It is distinct from the world in that her members are the subjects of King Jesus, and are loyal to him above all other loyalties.
3) the church is catholic - that word, was first used by Ignatius in about the year 105. The word is a compound of two Greek words, kata (according to) and holos (the whole). This has far reaching implications, but it means that any local church that is a part of the one church is also the whole church in that location. It is because of the church's catholicity that Paul's letters tot he Corinthians are just as valid and valuable to us as they were to them.
4) Lastly, the church is apostolic. If is build on the revelation of Jesus given to the apostles, which is the completion and interpretation of the Old Testament prophets.
What all this means is that the real church (and real local churches) are not the inventors or owners of the Christian faith, but are the custodians of stewards of it who are tasked with passing it on to the next generation of stewards.