Brain Drain

What Does Brain Drain Mean?
A slang term for a significant emigration of educated or talented individuals. A brain drain can result from turmoil within a nation, from there being better professional opportunities in other countries or from people seeking a better standard of living.

Investopedia explains Brain Drain
Brain drains cause countries to lose valuable professionals. The term is usually used to describe the departure of doctors, scientists, engineers or financial professionals. When these people leave, their country is harmed in two ways. First, expertise is lost with each emigrant, diminishing the supply of that profession. Second, the country's economy is harmed as each  professional represents surplus spending units. Professionals often earn large salaries, so their departure removes significant consumer spending from the country.