Musaf, Hebrew for "addition", is the additional prayer service of Judaism, recited on Sabbaths, festivals, the New Moon and the High Holy Days, but not on ordinary weekdays. It corresponds to the additional sacrifice that the Torah prescribes for these special days in the ancient Temple, over and above the daily offerings, and its recitation stands in place of that offering now that the Temple no longer stands. Musaf is prayed after the Torah reading of the morning service, following directly on Shacharit, so that on a Sabbath or festival the two run together into one extended morning of worship.
At its heart is a special Amidah, the standing prayer of benedictions, whose central section recalls the additional sacrifice of the day and voices the hope for the restoration of the Temple and its offerings. On the High Holy Days the Musaf Amidah is greatly expanded: the Rosh Hashanah Musaf contains the three great thematic sections on God's kingship, remembrance and the sounding of the ram's horn, and the Yom Kippur Musaf includes the solemn recollection of the ancient Temple service of the Day of Atonement. Because it is tied to the sacrificial system, Musaf has been treated differently by the more liberal Jewish movements, some of which have revised or omitted its petitions for the restoration of animal sacrifice while retaining the service.