Noun
Mussaf (plural Mussafim)
(Judaism) An additional prayer service recited on holy days (Shabbat, Yom Tov, Chol HaMoed, and Rosh Chodesh).
In addition, the Amidah prayer traditionally replaces the Temple's daily tamid and special-occasion Mussaf (additional) offerings (there are separate versions for the different types of sacrifices ). Source: Internet
This takes place either after the morning's Torah reading or at the end of Mussaf. Source: Internet
On Festival days and Sabbaths, instead of concluding the morning service, it precedes the Mussaf service. Source: Internet
The morning prayers are followed by an added prayer (Mussaf) as on all other holidays. Source: Internet