The 2001 Local Government Ordinance provides for devolution of government to district administrations. (Districts are the third tier of government, being sub-divisions of provinces. Prior to the Local Government Ordinance they were known as sub-divisions.) Each district administration is headed by a District Coordination Officer (DCO] and a Zila Nazim.
The District Coordination Officer is the administrative head of the District Administration. They have wide-ranging responsibility for overseeing, improving and directing the approved plans of the District Government.
The Zila Nazim used to be the executive head of the District Administration up until 2010, when the government gave their powers to the District Coordination Officers also. Their role is similar to district governor or prefect, with responsibility for implementing government strategy and developing initiatives arising out of it.
More information on the Wikipedia page .