Here below is a fuller Catechism quote...which explains what is meant by "Liturgy"...simply put it is official worship of the Church as the Body of Christ (Holy Mass being the most important part of the Liturgy...but also includes all the Sacraments, and Services such as Benediction, Easter Triduum Liturgies/Services during Holy Week, Liturgy of the Hours (Breviary) etc. ...vice a devotional services (Stations off the Cross) and private/groups or apostolates (Charismatic prayer groups, Rosary prayer groups or Divine Mercy chaplet prayer groups)..etc.. Also, note in the Eastern Rites...the word Liturgy...is usually applied to/means only...the Rite's Celebration of the Liturgy of the Word and the Liturgy of the Eucharist (called The Holy Mass by us in the Latin Rite)...they do not use the word Mass but their rite's name (e.g., Byzantine) and the word "Liturgy".
In the Liturgy...it is always the Body of Christ the Head which is Christ Himself...the Priest In Persona Christi...is this visible sign that Christ is the Celebrant...and the rest of the body....is all the faithful...whether physically present or not (even when praying the Liturgy of the Hours you are in communion with the whole Church...Christ, Pope, bishops, priests, deacons, religious who are all praying the Liturgy of the Hours)...we are all participants...we are always part of Christ's Body...thus Christ is One...thus only One Head and One body make up the Body of Christ....both in Time and in Eternity.
The other important aspect of Liturgy...with the One Christ Celebrating...(Head and Body)...the One Church is present/celebrating in the Worship of God...the Church Militant (here on earth)...the Church Suffering (the Poor souls in Purgatory)....and Church Triumphant (All those in Heaven)...so when the priest says at the beginning of Holy Mass..."let us prepare ourselves to celebrate these sacred mysteries"...he ain't kidding...he is not just using lofty words...he is saying something that is so profoundly mysterious....mystical...and powerful...we are entering into the Power and Authority of Christ made present.
Catechism of the Catholic Church
**What does the word liturgy mean?
1069 The word "liturgy" originally meant a "public work" or a "service in the name of/on behalf of the people." In Christian tradition it means the participation of the People of God in "the work of God." 5 Through the liturgy Christ, our redeemer and high priest, continues the work of our redemption in, with, and through his Church.
1070 In the New Testament the word "liturgy" refers not only to the celebration of divine worship but also to the proclamation of the Gospel and to active charity. 6 In all of these situations it is a question of the service of God and neighbor. In a liturgical celebration the Church is servant in the image of her Lord, the one "leitourgos"; 7 she shares in Christ's priesthood (worship), which is both prophetic (proclamation) and kingly (service of charity):
[INDENT]The** liturgy then is rightly seen as an exercise of the priestly office of Jesus Christ. It involves the presentation of man's sanctification under the guise of signs perceptible by the senses and its accomplishment in ways appropriate to each of these signs. In it full public worship is performed by the Mystical Body of Jesus Christ, that is, by the Head and his members.** From this it follows that every liturgical celebration, because it is an action of Christ the priest and of his Body which is the Church, is a sacred action surpassing all others. No other action of the Church can equal its efficacy by the same title and to the same degree. 8