Informally, the Southern Baptist Convention is a denomination made up of cooperating churches. That is how it is likely most often used in general conversation. The convention site itself describes the SBC as a fellowship. "The Southern Baptist Convention (SBC) is a fellowship of over 47,000 Baptist churches scattered across the United States and its territories." More technically, the Southern Baptist Convention is the annual June two-day convening of the messengers of the churches. "Article III. Composition: The Convention shall consist of messengers who are members of Baptist churches in cooperation with the Convention." The SBC also uses languages that is a "missional organization."
Among the many on the BB who are members of churches that cooperate in the Southern Baptist Convention, I am not one. I have both attended and preached at Southern Baptist churches, have family members who are members of Southern Baptist churches, but I have never been a member of a church participating in the SBC. Our church is unaffiliated with any organized groups. While I judge an individual church by the church itself, it is unlikely that I would ever join a Southern Baptist cooperating church. Part of my opinion of the SBC as an organization is that it is too large, made up of too many diverse elements (beliefs), yet at the organizational level usually led by pastors (or members) of large churches (think, J. D. Greear, Russell Moore, David Platt) who do not best represent the rank and file of the body.
The average SBC church doesn't even know who Grear is