For those who may not know (from Wikipedia):
Ash Wednesday is the first day of Lent in the Western Christian calendar. Occurring 46 days before Easter, it is a movable fast that can fall as early as February 4 and as late as March 10.
According to the canonical gospels of Matthew, Mark and Luke; Jesus spent 40 days fasting in the desert, where he endured temptation by Satan. Ash Wednesday marks the beginning of this 40-day liturgical period of prayer and fasting. Of the 46 days until Easter, six are Sundays and Sundays are considered "feast" days during Lent.
Ash Wednesday derives its name from the practice of placing ashes on the foreheads of adherents as a reminder and celebration of human mortality, and as a sign of mourning and repentance to God. The ashes used are typically gathered from the burning of the palms from the previous year's Palm Sunday.
Here's a fellow I like to read, regarding Ash Wednesday from a Baptist perspective.
This practice is common in much of Christendom, being celebrated mainly by Catholics, Anglicans, Lutherans, and Methodists.
Praise His Holy Name!