In the Roman Catholic Church, Ash Wednesday is the first day of Lent, the season of preparation for the resurrection of Jesus Christ on Easter Sunday. (In the Eastern Catholic Churches, the first day of Lent is Clean Monday.)
Ash Wednesday falls on February 10, 2018, 46 days before Easter 2018. (For more on why Lent is 40 days long but Ash Wednesday falls 46 days before Easter.