第三文化小孩是一个全球国际化的产物，意指一个“一个小孩，于一个或多个不属于自己的原有文化中，处于有影响的一段时间，接而将不同文化的特质及思想融入自己原有的文化之中”的人。这个人的文化背景是由家长的第一文化（双亲也有可能是不同文化的），和他成长当地的第二文化，所融合而成的第三文化。

随着国际间交流的性质，第三文化小孩出于下列几种家庭职业：传教（17%）、从商（16%）、政府机关（23%）、军事人员（30%）及其他（14%）。 至从于1960年代社会学家Ruth Hill Useem 使用此词，此次文化是被国际间的学者热烈研究的一门科目。通常这些第三文化的人会比较认同其他同背景的人，不论国籍，甚至过于同国非第三文化的人。

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. The definition is not constrained to describing only children, but can also be used to describe adults who have had the experience of being an ATCK (Adult Third Culture Kid). The experience of being a TCK is unique in that these individuals are moving between cultures before they have had the opportunity to fully develop their personal and cultural identity. The first culture of children refers to the culture of the country from which the parents originated, the second culture refers to the culture in which the family currently resides, and the third culture refers to the amalgamation of these two cultures. The third culture is further reinforced with the interaction of the third culture individual with another expatriate community one would come to encounter.