The "Liturgy" is commonly used in Christian services and can mean a service as ritual performed. Liturgy can also mean an arrangement of multiple services according to a particular order; a collection of various formularies; a specific form of Eucharist service; any Eucharist service; and a voluntary ancient public office in Athens (Random House Dictionary).
Using the church services as examples of those meanings of liturgy, during the Catholic Mass, "The Liturgy of The Word" is the section of the service that includes the Bible readings, which is ordinarily one Old Testament reading, one from the New Testament Epistles and always a Gospel reading. The "Divine Liturgy" is the Eucharist or Communion service.
The Book of Common Prayer is a Protestant Anglican collection of formularies of Liturgy. In both Catholic and Protestant churches, different "liturgies" are used according to, for example, a specific religious occasion or feast. The Liturgy, then, is the basis for the church service around which other liturgies may be developed.
In Eastern Orthodox Churches, there is the Byzantine Rite which includes the Divine Liturgies, regarding the preparation for and taking of Holy Communion. The Liturgy of the Catechumens is reserved only for those who have received the sacrament of Holy Communion.
The Liturgical Calendar begins on December 1 when Advent begins and builds up to the Birth of Christ and beyond as various events are recalled and celebrated, then ordinary, day to day calendar time, precedes the commencement of the new liturgical calendar on December 1 once again.