The term vicar has multiple meanings, and it has been used in Christian religions for thousands of years. The pope of the Catholic Church holds the title of Vicar of Christ, or Vicarius Christi. In essence, he is the earthly representative of God, and has received his appointment from Christ. The word "vicarious" can give a sense of what the term means: to live vicariously is to live without direct experience of something, but rather through something else. Someone can live vicariously through another person, through watching TV or reading books, to name a few examples. These things, which are not direct experiences, are the vicars of the person experiencing things second hand; they represent the experience without being the experience.
In fact, in various religions, the vicar is the vicarious symbol of the church, or better defined as a representative of a church. The term has since come to have many fine distinctions about a church leader or minister. It can also designate the status or training of a person working in a ministerial capacity in a church.
In the modern sense, a Lutheran vicar is essentially completing his internship and hasn’t received ordination. After having completed school, he will serve a parish for a year and is paid a small stipend for this service. This is his training ground, and the appointment he receives to a parish is almost always a year in length. He can then become a pastor or rector of a church, or stay on to assist the parish in which he began his work. This individual is paid by either the church in which he works or by a larger church structure.
Most commonly, the term is used in describing members of the Anglican and Episcopal clergy. The early vicar was designated as such depending upon how he was paid. Generally, a rector of a parish lived on the tithes and donations of a self-sustaining parish. The overhead organization of the Anglican Church would appoint a vicar, and pay him when a single church could not yet sustain itself.
Often, a newly organized church, which cannot yet sustain itself through donations, is called a mission. Its leader, as representative of the Episcopal or Anglican Church is the vicar of the mission. He will continue to receive a salary from the overhead organization until the church is well established and can afford to support a rector. At this point, he may become a rector, and derives all or at least most of his salary from the church he has established.
Today, the term is mostly in use in the UK, and most priests refer to themselves as ministers or clergy. Except with the Lutheran church, people are likely to see most ministers in Protestant denominations designate themselves as priests or ministers, since they act with the same authority, regardless of how their pay is structured. The term "rector" is still in wide use, since this person is normally the head of a single church and is generally in charge of the financial aspects of the church.