Triodion

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. 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:

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.

...
Wikipedia