According to the definition developed by Ruth Hill Useem, TCKs are people who have spent a significant part of their developmental years outside their parents' culture.[1] TCK is a broad term that encompasses all children who have grown up abroad (i.e. military kids, diplomats' kids, immigrants). Missionary kids are just one of the many categories of kids who qualify as TCKs. Therefore, while all MKs are TCKs, not all TCKs are MKs.