The Viddui confession is recited ten times during Yom Kippur. This count belongs to the traditional order of the day's five prayer services: Maariv, Shacharit, Mussaf, Mincha, and Ne'ilah.
In the usual explanation, Viddui is said once in the worshipper's silent prayer and again during the cantor's repetition, producing two recitations in each service. Maariv has no standard repetition of the Amidah, so its second instance is included in the communal Selichot that follows the evening prayer.
The confession is central to teshuvah, or repentance. Its two best-known forms are Ashamnu, an alphabetically arranged list of wrongdoing, and Al Chet, a longer confession beginning “For the sin.” The wording varies among Ashkenazi, Sephardi, and other rites.
A common mix-up is counting the additional confession recited before Yom Kippur begins. That can make the total appear to be eleven, but the conventional count for the day itself is ten. The number is also traditionally linked to the ten times the High Priest pronounced the divine name during the Temple's Yom Kippur service.