Epagomenal days - An intercalary month of five days (six days in leap years) in ancient Egyptian, Coptic, and Ethiopian calendars.
Ancient Egyptian calendar - A solar calendar with a 365-day year consisting of three seasons of 120 days each, and an intercalary month of five epagomenal days. The three seasons were relying on the variations of the Nile river from the flood to low waters.
Calendrier égyptien antique - Un calendrier solaire avec une année de 365 jours comprenant trois saisons de 120 jours chacune et un mois intercalaire de cinq jours dits épagénoménaux. Les trois saisons reposaient sur les variations du Nil, de l’inondation aux basses eaux.
"It is believed that the Egyptians greatly feared these days due to the prevalence of plague and disease, attributed to the wanderers (SmAjw) and slaughterers (xAtjw) of the goddess, Sekhmet, which were particularly rife at the end of the calendar year. Magical texts, such as the Book of the Last Day of the Year on Papyrus Leiden I 346, were recited in order to pacify the goddess, and rituals were performed, for example, the application of linen bandages inscribed with certain deities to the throat to ward off the effects of plague." (source: egyptianaemporium.wordpress.com)