A pastor is the head minister or priest of a Christian church, i.e., a parish. Many Protestant denominations use pastor as a title (e.g. Pastor Smith) or as a job title (e.g. Senior Pastor, Pastor of Worship, Children's Pastor, meaning the church leader in charge of those areas). The term is particularly common among denominations that believe in the priesthood of all believers and therefore reject the use of the term priest for their leaders. Such denominations include the Mennonites.
Catholic, Orthodox and Anglican churches typically refer to their leaders as priests, although the term "pastor" is used. In a Catholic parish big enough to have more than one priest, only one bears the title of pastor, and he is the head of the parish.