Generally used by the hyper-politically correct to obscure the fact that their father was career military.
Although there are a few exceptions, the term has little if anything to do with biracial, citizen-of-the-world, kumbaya style of multiculturalism that the user would want their gay socialist friends to believe. It is most commonly used as a smokescreen to explain their spending part of their childhood overseas under the umbrella of the evil Republican imperialist war machine.
"Wow, that's so cool. Was your mom in the Peace Corps or something?"
"Sort of... my dad was like with the government. My sister and I were like Third Culture Kids."
Seem pretentious? Too bad. They actually teach the term at some international schools.
"I grew up overseas. I'm a third culture kid!"
Third Culture Kids are often multilingual, very accepting and understanding of other cultures and good at adapting to new environments.
Third Culture Kids are most commonly the children of members of the military, international businessmen or diplomats, though the term can also be applied to the children of immigrants.
Notable TCKs include:
Barack Obama (Anglo-American mother, Nigerian father; raised in Hawai'i and Indonesia)
Kim Jong-il (Korean parents; raised in USSR, North Korea and China)
Keanu Reeves (English mother, American father; raised in Lebanon, Australia, USA and Canada)
Pete Docherty (British parents; raised in Northern Ireland, Germany, Cyprus and England)
How you tell your gay socialist friends that you grew up all over the world because dear old dad was a member of the evil imperialist war machine.