Canon (hymnography) in the context of "Magnificat"

Irmologion (Ancient Greek: τὸ εἱρμολόγιον heirmologion) is a liturgical book of the Eastern Orthodox Church and those Eastern Catholic Churches that follow the Byzantine Rite. It contains irmoi (οἱ εἱρμοί) organised in sequences of odes (αἱ ᾠδαὶ, sg. ἡ ᾠδή) and such a sequence was called canon (ὁ κανών 'law'). These canons of nine, eight, four or three odes are to be chanted during the morning service (Orthros). The name irmologion derives from heirmos (ὁ εἱρμός), which means 'link'. The irmos is a melodic model which preceded the composition of the odes. According to the etymology, the book 'collects' (λογεύω logeuō) the irmoi.

An Afterfeast, or Postfeast, is a period of celebration attached to one of the Great Feasts celebrated by the Eastern Orthodox Christian and Eastern Catholic Churches (somewhat analogous to what in Western Christianity would be called an Octave).

The celebration of the Great Feasts of the church year is extended for a number of days, depending upon the particular Feast. Each day of an Afterfeast will have particular hymns assigned to it, continuing the theme of the Feast being celebrated. At each of the divine services during an Afterfeast, the troparion and kontakion of the feast are read or chanted. The canon of the feast will usually be chanted on every day of the Afterfeast (if two canons were chanted on the day of the feast, they will be alternated on the days of the afterfeast).

The irmos (or heirmos from Koine Greek: εἱρμός) in the Byzantine liturgical tradition is the initial troparion of an ode of a canon. The meter and melody of an irmos is followed by the remaining troparia of the ode; when more than one canon is used (as is typical at matins), only the first canon's irmos is sung, but the irmoi of the subsequent canons must be known in order to determine an ode's melody and so, even in canons where it is known that the irmos is never sung, the irmos is nonetheless specified. Note that in the Russian tradition, often only the irmos is sung, the rest of the ode simply being read; in Greek parishes, often the remaining troparia are simply eliminated, but in non-Russian traditions, all troparia of a canon are sung

The term comes from the Greek verb "to tie, link" meaning that it poetically connects the Biblical ode to the subject of the canon.