SEDER (Heb. סֵדֶר; "order," "arrangement"). The word seder occurs only once in the Bible, in the plural (Job. 10:22), but it is extensively used in rabbinical literature. The best known of these uses are the following:
(1) The pericopes of the Bible according to the triennial cycle. These divisions are called sedarim, hence the Aramaic form sidra, popularly but wrongly used, particularly in Yiddish (sedra) for the weekly portion (instead of parashah).
(2) The six orders into which the Mishnah is divided. See Shas.
(3) An order of prayers. Although the word usually employed is siddur, that of R. Amram is properly called the seder of R. Amram.
(4) An order of service and worship. This is the most extensive use of the word. Thus there is reference to the seder of the benedictions (RH 4:5), of the sounding of the shofar (RH 4:9), and for fast days (Ta'an. 2:1), while the detailed description of the daily sacrifice concludes "thus was the seder of the daily offering in the service of the House of God" (Tam. 7:3). Similarly the service in the Temple is called the seder Avodah. The most common use of the word in this sense is the seder of Passover, which, in the piyyut on the conclusion of the prose part of the Haggadah is called siddur Pesaḥ (for a full description see Passover).