Definition(s):

“The emigration of highly skilled or qualified people from a country.” (Brain Drain, 2004).
“A nation’s or institution’s loss of scientific, technical, or leadership talent when these people relocate. This is a problem in developing countries, which use their limited resources to educate citizens only to see them migrate to nations that offer higher salaries or other desirable conditions.” (Barker, 2003, p. 50).
“…a situation that occurs when talented and highly skilled people migrate from one place to another, especially in search of advanced education and employment. It often occurs when young people migrate from Third World countries to Europe or the United States…The emigration of skilled and talented people has also been a problem for some advanced industriaThe Concise Oxford English Dictionary, Twelfth edition . Ed. Catherine Soanes and Angus Stevenson. Oxford University Press, 2008. Oxford Reference Online. Oxford University Press. Boston College Libraries.l societies, including Great Britain.” (Johnson, 2000, p. 30).

"brain drain n." The Concise Oxford English Dictionary, Twelfth edition . Ed. Catherine Soanes and Angus Stevenson. Oxford University Press, 2008. Oxford Reference Online. Oxford University Press. Boston College Libraries. 28 February 2011. Barker, R.L. (2003). The social work dictionary (5th ed.). Washington, DC: NASW Press. Johnson, A.G. (2000). The Blackwell dictionary of sociology (2nd ed.). Malden, MA: Blackwell Publishers, Inc.