The word liturgy has developed over many years. In classical greek, leitourgia is a work done on behalf of the people. In ancient times, any work that was done by someone for the good of the community could be considered a leitourgia. In the early church, liturgy referred to both the people involved in ministry (church officials) and the actual act of worship (see the New Dictionary of Sacramental Worship for more on this). If you want to read up on the most-up-to-date definition of liturgy, I’d suggest consulting the Constitution on Sacred Liturgy the Second Vatican Council. While the Council Fathers do not give a specific clear-cut definition of the word, this Constitution does provide us with many images and insights about the liturgy.