Ash Wednesday
Ash Wednesday is the Wednesday that is 46 Days before Easter, or 40 Days not counting Sundays. I am not sure why Sundays are excluded. Perhaps to get to this seemingly important number used so often in the Holy Bible.
On Ash Wednesday members of the Catholic Church allow a Priest to rub palm ashes on their foreheads. Perhaps other Religions also have this ritual. The ashes are often rubbed on the forehead in the shape of a plus sign, most probably indicative of the cross.
Ash Wednesday is Day after Fat Tuesday and is the start of Lent.