Ash Wednesday is a holiday marking the beginning of the season of Lent. In Catholicism, it is a Holy Day of Obligation, and doesn't exist for the Orthodox. Some Protestants observe the day, but many do not.
Ash Wednesday marks the start of the season of Lent, a time where one prepares for Easter, gives up something, takes something on, and spends Fridays fasting, representing the period when Jesus fasted for forty days and was tempted by the Devil. Because of the frequency of people giving up smoking for Lent, Ash Wednesday has also become "National Non-Smoking Day" in Ireland and pre-1984 UK.
On Ash Wednesday, there is a church service. Shortly before or after, the parishioners move forward to have their foreheads marked with ashes in the form of a cross. This symbolizes the ancient custom of sackcloth and ashes when one is mourning. Parishioners wear dark clothing and have a somber service. Many like to leave the ashes on for the duration of the day, but it's not an obligation. Many Protestants ridicule the practice, mistakingly calling it "dirt" and telling the Catholics to clean themselves. Protestants typically do not observe the use of ashes, but it is not unheard of for ashes to be put on ones head.
Before Ash Wednesday, parishioners are asked to donate their palm leaves from last years Palm Sunday to be burned to make the ashes. A popular "meme" has overtaken the Internet called "#AshTag" where people take photos of their ashed foreheads and post "selfies" with that "hashtag."
Christians are obliged to fast on Ash Wednesday, whether it be just one meal and no meat, or no meals at all.
Orthodox Equivalent Edit
Ash Wednesday is primarily a Western Christian observance, and is rarely seen in the East. The Orthodox instead opt to observe Clean Monday as their starting date for Great Lent, six weeks before Easter Sunday. Some Eastern churches observe it, but it is very rare.