Katavasia (pl. Katavasiae, from the Greek katabaino, "go down")
The Katavasia is the concluding hymn of an ode of a canon. The most commonly used katavasiae are taken from the Irmoi of the canons of Feast days. The one used on most Sundays of the year is taken from the canon of the service for the Akathist hymn, that is appointed for the fifth Saturday of Great Lent. On Sundays and feasts, there is a katavasia at the end of each ode, but on normal weekday services, there are only katavasiae at the end of the third, sixth, eighth, and ninth odes.
The katavasia takes its name from the practice of the choir coming down from the kliroi on either side of the Church, and singing this hymn in the center of the Church. This practice is still observed in some monasteries.