What are Third Culture Kids/Missionary Kids?

"Missionary Kids (or MKs) are the children of missionary parents, and thus born and/or raised abroad (that is, on the "mission-field"). They form a subset of Third Culture Kids (TCKs). Third culture kid (TCK) is a term used to refer to children who were raised in a culture outside of their parents' culture for a significant part of their development years."

https://en.wikipedia.org/wiki/Missionary_kid