halfpat's are people who have relocated to another country, taken developed a nearly native understanding of the language and culture by themselves. Normally used in regards to China's halfpat community.
Mr. Kerchner has been studying mandarin for 4 years and lived in hutong in Beijings slum for 5 years he is definitely a halfpat.
An expatriate who is not being provided a "package" (salary bump, housing allowance, car allowance, home leave, etc.) by his employer, and who perhaps is not even formally employed. Halfpats sometimes earn income as "English teachers" but are primarily engaged in the avoidance of real life in their home country.
Heckle: I thought Kevin worked for Pfizer?
Jeckle: Nah, he's a halfpat. Teaches English during the day and bangs his students at night.