A Yeongusaeng (lit. "research student") is a student studying at the (korean go institute?) to become a professional player.
The Japanese equivalent is called Insei, the Chinese student is called Yuansheng (院生 yuànshēng or yuan4 sheng1).
Some photos from a Korean Go School (one of the largest ones):
The main teacher of this school Mr. YongSuYoo, 7-dan is quite famous in Europe
See also Korean-style Insei League on KGS