The additional prayer service that follows the morning service on Yom Kippur is Musaf, also spelled Mussaf.
Musaf means “additional” and originated as a liturgical counterpart to the additional sacrifice offered in the Jerusalem Temple on Sabbaths, festivals, and other special days. On Yom Kippur, its central themes recall the Temple’s solemn atonement ritual, especially the service performed by the High Priest in the Holy of Holies.
The sequence can be confusing because Yom Kippur has an unusually long prayer schedule. Shacharit, the morning service, is followed by Torah reading and then Musaf. Later come Mincha and Ne’ilah, the closing service. Maariv belongs to the evening, while Hallel is a collection of praise psalms that is generally not recited on Yom Kippur because the day’s penitential character takes precedence.
The most distinctive section of Yom Kippur Musaf is the Avodah. It poetically recounts the ancient Temple ceremony, including the High Priest’s confessions, incense service, and entry into the Holy of Holies. This is a remembrance of a ritual no longer performed since the Temple’s destruction.