The loss of useful educated persons, esp professionals, because they can find better conditions elsewhere: Stalled Economy Speeds Puerto Rico's Brain Drain(1960s+ British)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with braindrain's
The departure of educated or talented persons for better pay or jobs elsewhere, as in The repression of free speech in Germany triggered a brain drain to Britain and America. The term originated about 1960, when many British scientists and intellectuals emigrated to the United States for a better working climate.