It's not just what you do in synagogue.
What is liturgy? In some ways, liturgy translates the Hebrew term avodah עבודה) ), which means worship (or work). Liturgy is, broadly, a description of the drama of worshipping God. Liturgy is not just the words that are recited, whether fixed or spontaneous, it also includes the actions, the occasions for the worship, and the gathering of the participants. Liturgy is in some ways akin to a screenplay, but just as screenplays have differing degrees of flexibility in the hands of different directors, so do different liturgical moments.
What is Liturgy?
Judaism has a broad range of liturgy: Worship in formal prayer in a synagogue at one of the appointed times with a quorum of at least ten adults (a minyan) is only one kind of Jewish liturgical expression, and it is not even the most common. The most common liturgical moments are the occasional blessings that a person recites upon performing certain commandments, or mitzvot (Birkot Mitzvah), or on eating, or on experiencing some wondrous aspect of nature (Birkot haNehenin). Rituals such as wedding ceremonies, the Passover seder, ritual circumcisions, and putting up a mezuzah (the box containing selections from the Torah) on a doorpost of a new home, are all liturgical activities that have their own choreography and texts.
The basic challenge of liturgy is that, on the one hand, we expect conversation with God to be intimate and real and spontaneous, as one might speak with a parent; on the other hand, we approach God with the images of royalty, and royalty has a defined protocol. Jewish law defines a requirement of three daily prayers with set liturgies, and it is very difficult to be spontaneous on a schedule with a familiar text. Through our history, Jewish liturgy has swung back and forth between these poles of the spontaneous and occasional (kavvanah, or true intention) versus the fixed and routinized (keva, or fixed and established). On the side of keva are the established texts that have been used for centuries: the siddur for daily prayer, the machzor for prayer on the High Holidays, the haggadah for the ritual of the Passover seder (the ritual meal on the first night or nights of Passover). On the kavvanah side are the new siddurim, machzorim, and haggadot (as they are known in their plural forms) that are continually published, along with the new commentaries, poetry, and melodies that are designed to accompany them, and the entire area of private, personal prayer.