Holiday music includes all music sung during an annual festival, national holiday, or religious event. Most of these were written in anticipation of or in commemoration of an event, season or time period. The biggest of these is the Christmas music category. Christmas (Xmas) music comprises a variety of musical genres which are normally heard or performed around the Christmas season (also known as the festive season or the holidays) which runs from late November to early January. Music originating with the pipe organ (now commonly played at Christmas piano music services), has always been a feature of the season and its respective celebrations, with the earliest examples being hymns (chants and litanies) for liturgical use in observance of the Nativity and Theophany.