Ash Wednesday falls on a Wednesday (no, duh) and begins a 46 day period of Lent leading up to Easter.
The day focuses on Jesus' 40 day period of fasting and praying in the desert where he was tempted by Satan.
Participants of Ash Wednesday are asked to abstain from something and focus on personal holiness. Ash Wednesday begins with a person going to church and getting ashes placed on their forehead as a sign of repentance. They are not supposed to wipe the ashes off, but let them slowly fade away.
Ash Wednesday follows FAT TUESDAY (or Shrove Tuesday/Pancake Tuesday) when people basically pig out and eat/drink all the things they are about to abstain from. MARDIS GRAS is the celebration leading up to this time of abstaining.
Ash Wednesday is never mentioned in the Bible, but it has elements that are certainly biblical.
"Therefore I despise myself and repent in dust and ashes.” Job 42:6
"For I eat ashes as my food and mingle my drink with tears." Psalm 102:9
Ashes represented death and mourning and became linked to one's despondency over their situation or sinfulness.
On the twenty-fourth day of the same month, the Israelites gathered together, fasting and wearing sackcloth and having dust on their head. Nehemiah 9:1
Nationwide fasting was a practice that occurred in the Old Testament, with people putting dust on their heads. All of it represented a desire to be holy and free of sin.
So if Ash Wednesday is a day of following Jesus by fasting for 40 days, with a sincere desire to be holy, repenting of one's sin, then Ash Wednesday has biblical overtones.
However, Jesus didn't party the night before the desert, creating a list of sins he needed to repent from.
People in the Bible who fasted and rolled in ashes were DEVASTATED by their sin. They did not want to return to their old ways ever. It was not just a 40 day period without alcohol, sugar or TV. They wanted to change their lives, not just good in God's eyes for over a month.