According to the Oxford Dictionary of the Christian Church the word 'Liturgy' is used in two senses:-
Firstly, it relates to all of the prescribed services of the Church, as contrasted with private devotions.
Secondly, and especially in the Eastern Church it describes the Eucharist.
In practice, liturgy is a set of responsive prayers that enable a congregation to participate in the dialogue of worship. In some traditions congregational participation is the norm and done freely and openly through words, song and action. To others it is not, and a liturgy enables a person to feel a part of the worship and prayer offering to God, in a way that they might not if it were all led from the front.