In the Church of England a vicar is the priest in charge of a parish, and the title preserves the memory of a particular medieval arrangement about who received the income of the parish.
Vicar and rector
Historically the distinction between a vicar and a rector lay in the tithes: the rector received the full tithe income of the parish, while in parishes whose tithes had passed to another party, a monastery or a lay holder, the cure of souls was served by a vicar, one who acted in the place of the holder of the tithes and received only a portion, so the title vicar, meaning one who stands in for another, records that the priest served on behalf of the party who drew the income. The distinction is now largely historical, and both vicar and rector are simply parish priests, but the two titles survive.
The office today
In modern usage the vicar is the incumbent priest of a parish, responsible for its worship, teaching and pastoral care, and the title is the one most familiarly associated with the Church of England parish clergy. The priest enters the office by ordination and appointment to the living. The office corresponds to the ordinary parish clergy of other Western churches, its particular name preserving the old arrangement of tithes rather than marking any present difference of function from the rector. The vicar thus represents the parish priest of the Church of England, and the survival of the title, alongside that of rector, is a small monument to the medieval history of how the income of parishes was divided.