Ash Wednesday is the first day of Lent in the Western Christian calendar. It occurs 46 days before Easter. The date is different each year because the date of Easter varies. It can fall as early as February 4 and as late as March 10.
Those able to and willing to should fast voluntarily between Ash Wednesday and Easter. There are exceptions, though. Pregnant women, sick people, children, and the old usually don't have to.
Ash Wednesday is a very important part of Lent.