That is what we discovered on Wikipedia concerning the Liturgy:

Liturgy is the customary public ritual of worship performed by a religious group. As a religious phenomenon, liturgy represents a communal response to and participation in the sacred through activities reflecting praise, thanksgiving, remembrance, supplication, or repentance. It forms a basis for establishing a relationship with God or the divine.

Technically speaking, liturgy forms a subset of ritual. The word liturgy, sometimes equated in English as "service", refers to a formal ritual enacted by those who understand themselves to be participating in an action with the divine.