What is a mainline church exactly??? That term is confusing because to me it implies on the straight path?
Pretty much any church with a denomiation. Baptist, Methodist, Episcopal, etc.
If you can call yourself anything other than "Christian" and have people recognize what you mean, chances are it's a mainline church. (ie, "I'm a Pentecostal", etc.)
"Mainline" is a term coined by the media to reference non-Evangelical, non-Fundamentalist and non-Catholic denominations.
Mainline Protestant denominations include Presbyterian, United Methodist and the Episcopal Church. The leadership of these bodies is almost completely liberal, far moreso than the people in the pews.
That is not to say that everyone who attends these churches agrees with the leadership. I have a friend who is a Prebyterian minister who is deeply devout and is quite conservative.
Everything else is not 'mainline': Assembly of God, Disciples of Christ, Covenant Church, Pentacostals, etc., etc.
Alright.....here it is......the UMC, ELCA, PCUSA, Episcopal Church.
Basically these are the biggies.....mainline means biggest of the Protestant denominations (they tend to be the most liberal).
There are more conservative branches of these churches that are not considered mainline, such as the Presbyterian Church in America or the Lutheran Church (Missouri Synod).
Lutheran, Congregational, Episcopal, United Methodist, some Baptist & some Presbyterians. They tend to be liberal in their theology & rules.
Other, newer conservative denominations have broken away from the above to form new ones. For instance, the Wesleyan Church broke away from the United Methodists over slavery in the 1860's. Those breaking away thought it was wrong.