In less developed countries, what does the brain drain refer to?

In less developed countries, people who get higher education tend to move to rich countries to get a chance for a better lifestyle and career path.
By doing this, brains tend to drain out from less developed countries.

Based on this, in less developed countries, the brain drains refer to:"The emigration of highly skilled workers to rich countries" 

This country likely has a high total fertility rate (tfr).

Asmall closed hole formed in an outwash plain or moraine. forms when a  glacier retreats then remains stationary.