Ash Wednesday is the first day of Lent in the Western Christian calendar, 46 days before Easter. The holiday derives its name from the practice of placing ashes on the foreheads of the faithful, as a reminder and celebration of human mortality and as a sign of mourning and repentance to God (Jesus spent, after all, 40 days fasting and resisting temptation by Satan in the desert for our sins — or that's what the scriptures say).
This year, Ash Wednesday is observed in the wake of Pope Benedict XVI surprising resignation. The occasion offers an opportunity for millions of Catholic worldwide to reflect on the future of a faith that has been marred with accusations of sexual abuse and a denial to embrace more progressive stances in social issues. Will the Roman Catholic Church take this opportunity to make some progress and embrace more liberal views (perhaps, appointing the first black pope would be a good start).
In the meantime, don’t freak out if you see people walking on the streets with a black ash cross on their forehead. It's not the Zombie Apocalypse, it's just Catholics (like myself) trying to observe an old tradition.