Ash Wednesday

In the Christian calendar, Ash Wednesday is the first day of Lent, and that's today.

It occurs forty days before Easter, not counting Sundays (which are not included in Lent); it occurs forty-four days before Good Friday counting Sundays. Its placement varies each year, according to the date of Easter. The date can vary from early February to as late as the second week in March.

This period has lots of European folklore associated with it. You can read about it here in the Book of Days.