Here is how Philip Melanchthon delineates the meaning of the church (ecclesia) in his Propositions embracing the chief articles of heavenly doctrine (CR 12, 399-400):

And according to this doctrine, I believe that there is a true church of God, which is the visible assembly that embraces the gospel; in this assembly, the Son of God as Mediator is efficacious through the ministry and regenerates many by the Holy Spirit, so that they may be his eternal inheritance. At the same time, however, there are many in this visible assembly who are not saints, who nevertheless agree with the saints in their profession of doctrine.

I do not play around with the trickery of interpretations, nor do I mix religions together into one chaotic mass, but I affirm that it is only in this church of our Lord Jesus Christ that forgiveness of sins, righteousness, and eternal salvation are given to men. And in the individual parts of doctrine I faithfully maintain the sense in which they are understood in the catholic church of God, and I condemn all the madness that is condemned by the judgments of the catholic church of God, namely, pagan, Epicurean, Stoic, Academic, and similar madness; likewise, Jewish, Muslim, Ebionite, Machichean, Arian, Pneumatomachic, ^[1] Pelagian, Novatian, and Donatist madness; as well as magic and the worship of idols–pagan and, more recently, that of the pope and the monks. And I give thanks to God that he has led me out of this darkness and has placed me in his church. And I profess that I am a member of the church of God and of our Lord Jesus Christ, and I call upon God with the whole church that thinks righty, which I do not fashion as a Platonic Form, but I say that it is the visible assembly in which the Word of the gospel sounds forth uncorrupted; of this assembly, the church of these regions in which I live is itself a member, although in it, too, there is great weakness.”

The translation is my own.