The term 'Third Culture Kid' (TCK) was first used by Ruth Hill Useem in her research on American children living in India. The term is applied to people who have grown up in a country, or several countries, other than the one(s) that their parents grew up in. There are a couple of other names for specific types of TCKs; a 'Corporate Kid' for instance is a child whose parents had to move frequently for business reasons. Other types include 'Missionary Kid,' or 'Army Brat.' As a whole they are often referred to as 'Global Nomads,' and the defining characteristic of them all is that they spent a significant amount of their developing years in a country other the one(s) that they have citizenship in.
As a result of constantly having to move around, or being exposed to different cultures within and outside of their family, TCKs usually find it very difficult to identify with any specific culture. They tend to have more in common with each other than with those who they happen to have the same citizenship. Their roots are not embedded in a place, but in people. Usually the most stable thing in a TCK's childhood is their family; many of them would have had to leave their friends behind every time that they leave a country.
These constant changes usually lead to a very specific type of person, one who is very independent and self-reliant, often a loner. That self-reliance can be turned into an asset as a TCK grows up and enters the business world. However, this independence often verges on isolation - the pain of having to leave behind friends so many times in childhood may lead them to feel that they do not need or want to have any close relationships. When they leave a country, they tend to let go of the friendships that they have formed far more easily - they lose touch with their old friends a lot more quickly than most people would.
A TCK can never turn back into a mono-cultural person, and for the majority of their lives they may choose a similar life to that which their parents chose. They are usually very tolerant of differences between themselves and other people, and are often extremely friendly and good at making friends quickly - something they have learnt because of much practice. Unsurprisingly TCKs tend to be good with languages, a skill that they have often learnt out of necessity. They find it far easier to change their behavior, language and actions based on the situation due to the fact that they will have often had to do this many times in the past.
Whilst there may be benefits to having such a lifestyle, there are of course consequences. TCKs often feel no sense of belonging to any particular place, so they often spend their adult lives traveling from one place to another to try and find where they can belong. They often have no qualms in losing a relationship, sometimes finding it preferable than having to spend time trying to solve problems that may have arisen in a relationship. Often the parent's of TCKs express frustration at the fact that they do not identify with the same country as the parents do.