-ksen
Liturgy is a set form of public worship. It is what we do when we gather to worship. Unless your church follows no form or manner of worship, you have a liturgy, too. Some churches follow a more highly structured liturgy than others, but I doubt there are many churches who have no form whatsoever.
Our Sunday liturgy consists of hymns, prayers (some said by all, some said by the priest on behalf of all), bible readings, a sermon, the creed, and of course communion.
Merriam-Webster says, "Greek leitourgia public service, from Greek (Attic) leïton public building (from Greek laos -- Attic leOs -- people) + -ourgia -urgy"
The Greek word appears in Scripture, although at the moment I can't tell you where. The Orthodox understanding is that the Liturgy is the common spiritual work of God's people. Here's a couple of passages that make it clear the reverence we have towards Liturgy:
"The word liturgy means common work or common action. The Divine Liturgy is the common work of the Orthodox Church. It is the official action of the Church formally gathered together as the chosen People of God. "...It is the action of the Church assembled by God in order to be together in one community to worship, to pray, to sing, to hear God's Word, to be instructed in God's commandments, to offer itself with thanksgiving in Christ to God the Father, and to have the living experience of God's eternal kingdom through communion with the same Christ Who is present in His people by the Holy Spirit.
"...The Divine Liturgy is not an act of personal piety. It is not a prayer service. It is not merely one of the sacraments. The Divine Liturgy is the one common sacrament of the very being of the Church Itself. It is the one sacramental manifestation of the essence of the Church as the Community of God in heaven and on earth. It is the one unique sacramental revelation of the Church as the mystical Body and Bride of Christ.
"...In the New Testament Church Jesus Christ is the Living Word of God, and it is the Christian gospels and apostolic writings which are proclaimed and meditated at the first part of the Divine Liturgy. And in the New Testament Church, the central saving event is the one perfect, eternal and all-sufficient sacrifice of Jesus Christ, the one great High Priest who is also the Lamb of God slain for the salvation of the world, the New Passover. At the Divine Liturgy the faithful Christians participate in the voluntary self-offering of Christ to the Father, accomplished once and for all upon the Cross by the power of the Holy Spirit. In and through this unique sacrifice of Christ, the faithful Christians receive Holy Communion with God."
The online source is: The Divine Liturgy, if you would like additional information. Christ Bless.