Hikikomori (窶堙絶?堋ォ窶堋ア窶堙?窶堙ィ or ヒ?ク窶堋ォヒ弑窶堙ィ lit. "pulling away, being confined," i.e., "acute social withdrawal")
Hikikomori - Wikipedia
I'm surprised that there's already an article on it in English version of Wikipedia!
(browsing the English page)
Ah, it is not something unique to Japan, similar phenomenon is observed in other countries as well..