According to the Western Christian Calendar, Ash Wednesday marks the beginning (first day) of Lent, that falls 46 days before Easter. It is 40 days to be precise because Sundays aren't included in the count.
Since it falls before Easter, its date varies every year in accordance with Easter. It could begin on any date between 4 February and 10 March.
The period of Lent for Christians is a time for fasting, remorse, self-discipline and spirituality. Its like preparing for the day of Easter.
The name Ash Wednesday comes from both history and culture. Ashes have been used since old times as a symbol of repentance and mourning. People rub themselves with ashes to express regret for sins. The ritual is still followed by certain Churches where on this day the minister rubs the holy cross with ashes and applies it on devotees' foreheads.