Ash Wednesday, in the Western Christian calendar, is the first day of Lent and occurs forty-six days before Easter, in 2021 at the 17th of February. It is a moveable fast, falling on a different date each year because it is dependent on the date of Easter. It can occur as early as the 4th of February (5th of February on leap years) or as late as the 10th of March.
Ash Wednesday derives its name from the practice of placing ashes on the foreheads of adherents as a sign of repentance. The ashes used are typically gathered after the Palm Crosses from the previous year's Palm Sunday are burned. In the liturgical practice of some churches, the ashes are mixed with the Oil of the Catechumens (one of the sacred oils used to anoint those about to be baptized), though some churches use ordinary oil. This paste is used by the minister who presides at the service to make the sign of the cross, first upon his or her own forehead and then on those of congregants. (With material from Wikipedia)