Give some stream of consciousness and then the answer. Ash Wednesday is a Christian holy day of prayer, fasting and repentance. It is preceded by Shrove Tuesday and falls on the first day of Lent, the six weeks of penitence before Easter. Ash Wednesday is observed by many Western Christians, including Anglicans, Lutherans, Old Catholics, Methodists, Presbyterians, Roman Catholics, and some Baptists.

Based on this passage, what do we call the first day of lent?
To answer this question, we should know that: It is preceded by Shrove Tuesday and falls on the first day of Lent, the six weeks of penitence before Easter.
Therefore, the answer is Ash Wednesday.