The Church Calendar, also known as the Liturgical Calendar, is a set of dates and times that are used to organize the liturgical year. It includes important religious holidays and feast days, as well as the seasons of the church year. The two main components of the Church Calendar are the Ordo and the ROTA. The Ordo is a book that contains the dates and times of the liturgical year, while the ROTA is a list of the readings and prayers for each day. Together, these two components provide the structure for the Church Calendar.