Tachanun or Taḥanun (תחנון "Supplication"), also called nefilat apayim (נפילת אפיים "falling on the face"), is part of Judaism's morning (Shacharit) and afternoon (Mincha) services, after the recitation of the Amidah, the central part of the daily Jewish prayer services. It is also recited at the end of the Selichot service. It is omitted on Shabbat, Jewish holidays and several other occasions (e.g., in the presence of a groom in the week after his marriage). Most traditions recite a longer prayer on Mondays and Thursdays.
There is a short format of Tachanun and there is a long format. The long format is reserved for Monday and Thursday mornings, days when the Torah is read in the synagogue. The short format, recited on other weekdays mornings and on weekday afternoons, consists of three (in some communities two) short paragraphs.
According to the Nusach Sefard and most Sephardic rites, Tachanun begins with vidduy (confessional prayer) and the Thirteen Attributes; in Spanish and Portuguese and some Moroccan communities, these are recited only in long Tachanun. In this prayer several sins are mentioned and the heart is symbolically struck with the right fist during mention of each sin. This is followed by the mention of God's thirteen attributes of mercy. By and large, Sephardim do not rest their head on their hand for Kabbalistic reasons, but Spanish and Portuguese Jews and some Moroccans, who never accepted many Kabbalistic customs, do rest their head on their hand.
In most Nusach Ashkenaz communities, Tachanun begins with introductory verses from II Samuel (24:14), and then continues with a short confession that we have sinned and God should answer our prayers, followed by Psalm 6:2-11, which King David composed - according to traditional sources - while sick and in pain. In most Nusach Sefard communities, they also recite these verses, although only after reciting Vidui and the Thirteen Attributes.
In the Sephardic rite, Italian rite and Romaniote - adopted also in some Nusach Sefard communities, including Chabad - Psalm 25 is recited as Tachanun.