Like many other 'churchy' words, 'liturgy' comes from the language used by the early church in its worship and writings - Greek. The word liturgy is derived from leitourgia which was used to refer to any public work or function exercised by the people as a whole. The people who do the work of liturgy are the people of God, all baptised.
A well-known word that is close in meaning to 'liturgy' is the word 'worship'. But while worship can be done privately, 'liturgy' is always a public, group activity.
A working definition of 'liturgy' that is helpful is 'The official, public worship of the Church'.
Some of the best-known forms of liturgy in the Roman Catholic Church are Mass (or Eucharist), Baptism, Confirmation, Marriage, Funerals and Penance (or Confession). In the Catholic Church, we worship using forms and patterns of worship that have developed during the Church's 2000-year history. Every day of the year falls into a particular place into the church's liturgical calendar, and certain scripture readings and prayers are assigned for use at Mass each day. The celebration of the rites of Baptism, Marriage, Funerals and so on are set out in the Church's ritual of books.
Liturgy is always an action, something we do. It is a public action, a ritual action, and a symbolic action. It is the proclamation of the word that God speaks to us; it is in the breaking of the bread that we recognise Christ. We participate in the action of the liturgy by responding, singing, listening and joining the gestures.