What is "tachanun"

Tachanun or Taḥanun ( Hebrew: תחנון "Supplication"), also called nefilat apayim ("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. Traditionally, only the first four words of the prayer are said aloud so that others take notice. 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.