Short answers, pulled from the story.
Human capital flight describes the movement of highly trained individuals from one country to another. The term brain drain refers specifically to the negative economic impact on the sending nation when skilled workers leave.
Albert Einstein emigrated permanently to the United States in 1933 to escape Nazi persecution. He became a prime example of this phenomenon as a highly trained individual moving for safety.
The Royal Society coined the phrase brain drain to describe the exodus of scientists and technologists from post-World War II Europe. They used this terminology to track the flow of talent toward North America during the late 1940s.
Adult Haitians living in OECD countries sent about $1,700 per migrant annually back home. This amount exceeds double Haiti's per capita GDP of $670 at the time.
German universities suffered a loss of 20.5% of their teaching staff after the Nazi seizure of power. About 70% of fired scientists lost their position due to Jewish or non-Aryan ancestry.