Leadership is there in the list of spiritual gifts in Romans 12:8. It is a gift of grace from God the Holy Spirit, to the church, to be used with zeal. And, like with any spiritual gift from the Lord, it is crucial to release it to be used for the sake of building up the body to the maximum extent that it can be used.

It follows, then, that leaders are not:

merely representatives or employees of the congregation to fulfil the congregations list of wants and wishes
defined by denominational accreditation (although they may be recognised by such)
produced by simply giving someone a theological education. Give someone without spiritual gifts for leadership a theological educator and what you get is not a leader but an educated non-leader
people who happen to have certain paper credentials. Never confuse being called and qualified by God with being credentialled by man. They aren't the same thing
defined by who is authorised to do the sacramental bit

etc, etc, etc

I had a fascinating conversation with an anglo-catholic priest who seemed to think that spiritual gifts, including leadership, are conferred (exclusively) by the act of ordination. I can't imagine what he must have been taught.

What it reveals, however, is a close connection between the ability to exercise the gift of biblical spiritual leadership and (a) your church's ecclesiology, and (b) your church's understanding of spiritual gifts. If a church (or even a significant minority within it) insist that the role of the leader is to fulfil all their wishes for caring internally for their needs, you can't properly exercise a gift of spiritual leadership there (ie they have an institutional or "christendom" model of being a disciple - gathering to receive from the professional, rather than being equipped to be disciples). Similarly, if a church doesn't think that leadership is a spiritual gift, you can't easily do it there either. (ie people will think it is about activity running and maintaining the organisation they like, rather than leading a missional community into the plans and purposes of God for them. Casting vision, bringing discernment, laying sound doctrinal foundations, teaching the Bible, shepherding and leading the flock.)