An established formula for public worship, or the entire ritual for public worship in a church which uses prescribed forms; a formulary for public prayer or devotion. In the Roman Catholic Church it includes all forms and services in any language, in any part of the world, for the celebration of Mass.
The Eucharistic mystery stands at the heart and center of the liturgy since it is the fount of life by which we are cleansed and strengthened to live not for ourselves but for God and to be united in love among ourselves. Pope Paul VI
Liturgy is like a strong tree whose beauty is derived from the continuous renewal of its leaves, but whose strength comes from the old trunk, with solid roots in the ground. Pope Paul VI
We cannot build up the idea of the apostolate of the laity without the foundation of the liturgy. Dorothy Day
The real 'action' in the liturgy in which we are all supposed to participate is the action of God himself. This is what is new and distinctive about the Christian liturgy: God himself acts and does what is essential. Joseph Ratzinger
Second, we also got a more authentic liturgy of the people of God, in the vernacular language. Hans Kung