What is "koiak"

Koiak /ˈkʰɔjæk/ ( Coptic: Koiak /ˈkɔjak/ or Kiahk /ˈkijaxk/), is the fourth month of the Coptic calendar. It lasts between 10 December and 8 January of the Gregorian calendar. The month of Koiak is also the fourth month of the Season of Akhet (Inundation) in Ancient Egypt, when the Nile floods historically covered the land. They have not done so since the construction of the High Dam at Aswan.