A day that is especially sacred to a particular religion, over and above regular days of worship. Usually commemorates some divine act, such as a smiting of Pharoah's sons or an apotheosis.

In Gloranthan metaphysics, a god's rune associations can usually be plotted against the week, weekday, and season (see The Gloranthan Calendar). The High Holy Day is the day in the week of the season most appropriate to that god's rune associations. Yelm, for example, is associated with Death, Fire, and Fertility Runes. His High Holy Day falls on Fireday, in Harmony Week, in Fire Season.
Darkness cults celebrate High Holy Nights.