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The Triodion (Greek: Τριῴδιον, Triōdion; Slavonic: Постнаѧ Трїωдь, Postnaya Triod; Romanian: Triodul, Albanian: Triod/Triodi), also called the Lenten Triodion (Τριῴδιον κατανυκτικόν, Triodion katanyktikon), is the liturgical book used by the Eastern Orthodox Church.[note 1] The book contains the propers for the fasting period preceding Easter and for the weeks leading up to the fast.
The canons for weekday Matins in the Triodion contain only three odes and so are known as "triodes" after which the Triodion takes its name. The period which the book covers extends from the Sunday of the Publican and Pharisee (the tenth week before Pascha (Easter): twenty-two days before the beginning of Great Lent), and concludes with the Midnight Office of Holy Saturday.
The Triodion contains the propers for:
- the Pre-Lenten period, begins with a week in which there is no fasting, including on Wednesdays and Fridays, which are normally kept as fast days throughout the year (with few exceptions).
- The following week is called the Apókreō (literally: the "Leave-taking from Meat") in Greek. It coincides with the Carnival celebrations which, although officially discouraged by the Church as pagan remnants, are very popular. The Apokreo marks the change of diet to the fasting practice of Lent: meat is no longer eaten after the "First Apokreo Sunday" (i.e. the 8th Sunday before Easter), while for the following week, the Tyrinĕ, that culminates on Tyrinē Sunday (literally: "Cheese Sunday" or "Second Apokreo Sunday") just before Clean Monday, milk and dairy products, but not meat or eggs, may be eaten.
- the Forty Days of Great Lent itself, which begin on Clean Monday and for which a vegan type diet, with the addition that on many days the use of oil is excluded as well ("the Lenten Fast"). On two specific feasts during Lent (the Annunciation and Palm Sunday), fish is allowed. The fast is prescribed until Easter. This period coincides with the springtime birth of new lambs.
- Lazarus Saturday and Palm Sunday
- Great and Holy Week (up to and including the Midnight Office of Great and Holy Saturday)
In the edition of the Lenten Triodion used by the Old Believers and those who follow the Ruthenian recension, the contents of the Triodion end with the service of Lazarus Saturday and do not contain the services of Holy Week, which are to be found in the Pentecostarion.