The siddur is the prayerbook used by Jews the world over, containing a set order of daily prayers. Some siddurim have only prayers for weekdays; others have prayers for weekdays and Shabbat (the Sabbath); many now have prayers for weekdays, Shabbat, and the three Biblical festivals, Sukkot, Shauvot? and Pesach?. Such a complete siddur is referred to as a Siddur Shalem.
There are many additional liturgical variations and additions to the siddur for the Yamom Nora'im (The Days of Awe; the High Holy Days, i.e. Rosh HaShanah? and Yom Kipur). As such, a special siddur has developed for just this period, known as a machzor.
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