Avinu Malkeinu, (Hebrew:
אָבִינוּ מַלְכֵּנוּ),
translating to Our Father, Our King, is a prayer that
is recited during
Jewish services from
Rosh Hashanah to
Yom Kippur and on certain
public fast days at other times of year. Each line of
the prayer begins with the words "Avinu Malkeinu," followed
by varying phrases for the remainder of the verse.
On most days when Avinu Malkeinu is recited, it is included during Shacharit and Mincha on that day. But on Yom Kippur, Avinu Malkeinu is also recited during Maariv and Ne'ila, except when Yom Kippur falls on Shabbat, in which case, Avinu Malkeinu is recited during Ne'ila only. Other than Ne'ila, Avinu Malkeinu is never recited on Shabbat.
Throughout the Ten Days of Repentance, five lines of Avinu Malkeinu that refer to various books include the word Katveinu translating to "inscribe us." During Ne'ila, this is replaced with Chatmeinu, translating to "seal us."
Source: Wikipedia
