Ministry is often defined as "spiritual work or service." As it says in 1 Peter 4:10, "As each has received a gift, use it to serve one another, as good stewards of God’s varied grace." But I think it's more than serving; I think ministry has a way of giving back and blessing us in return.
The key is, ministry is relational. It requires community, however big or small.
In fact, I believe the heart of ministry is community - a sense of connectedness, fellowship, and unity; shared responsibility and ownership. If we aren't united in our mission and work together as a choir, what kind of ministry do we have?