A term that originated out of the common mistreatment and social ostracism of redheaded individuals (gingers). A redheaded individual born into(legitamately or not), or adopted into a family of non-redheads was typically subject to physical and emotional abuse, and usually short handed when it came to financial matters in the family, such as the estate or any savings the family had acquired. Today, the term can be applied to an individual or group of individuals who are outcasts, or are typically dealt the worst hand in society.
A stepchild might be singled out for abuse. But a red-headed stepchild (who presumably looks like his or her absent birth-parent) might be abused even more because he or she is so obviously different from the other children.
Myles was the red-head step child of the family, he was never invited to the family reunions.