This week is Holy Week for Christians, including Holy Wednesday, Maundy Thursday and Good Friday before celebrating Easter on Sunday, April 21. But mark your calendar for some lesser-known of this week's holidays, including High Five Day. It's almost hard to imagine a sporting event without the high-five, but the gesture really hasn't been around that long. This Thursday, April 18, is High Five Day, a day to mark the most famous of all celebratory gestures. But when and where did the high-five begin?