Hikikomori, lit. 'pulling away, being confined', i.e., 'acute social withdrawal', is a Japanese term to refer to the phenomenon of reclusive individuals who have chosen to withdraw from social life, often seeking extreme degrees of isolation and confinement because of various personal and social factors in their lives[….]

Although there are occasions when the hikikomori may venture outdoors, usually at night to buy food, the Japanese Ministry of Health, Labour and Welfare defines hikikomori as individuals who refuse to leave their parents' house and isolate themselves from society for a period exceeding six months. While the degree of the phenomenon varies on an individual basis, in the most extreme cases, some youths remain in isolation for years or even decades. Often hikikomori start out as school refusals or futoko in Japanese.

From Hikikomori, Wikipedia entry