A prayer book for the High Holidays.
Although we tend to unite Rosh Hashanah (the New Year) and Yom Kippur (the Day of Atonement) in our thinking as the High Holidays or the Days of Awe, the two holidays are distinct in their themes and observance. Nevertheless, the liturgical texts for the two holidays often are put into one book, the High Holiday Machzor (literally "cycle," here "festival prayer book"), and this forces us to look at the two holidays together.
The first page of a Rosh Hashanah Mahzor
The Rosh Hashanah service is distinguished from the standard festival prayer services in five major ways.
1) the use of a distinctive set of beautiful melodies,
2) the inclusion of lots of liturgical poetry (Piyyut, plural: Piyyutim),
3) the recitation of the prayer "Avinu Malkenu" (Our Father, Our King)
4) the blowing of the shofar (the ram's horn), and
5) the recitation, in the Musaf ("additional") service, of verses on the themes of God's sovereignty (Malkhuyot), God's consciousness of humanity and the Jewish people (Zikhronot, literally "memories"), and God's past and promised redemption (Shofarot, referring to the shofar as a symbol or herald of that redemption).
Only the last four leave their mark on the text in the Machzor. The liturgical poetry, which in medieval times was a standard part of the Shabbat or festival prayers but which nowadays is only common on the High Holidays, has been inserted in three main places: in the first blessing before the recitation of the Shema, and in the reader's repetitions of the Amidah during both the morning service (Shaharit) and the Musaf service. These focus primarily on images of judgment and God's kingship; these themes also pervade the Avinu Malkenu, which is recited after the Amidah of the morning service.