Hikikomori is Japanese for "pulling inward, being confined". The Japanese Health, Labor and Welfare Ministry defines hikikomori as people who haven't left their house or had real social interaction for six months or more.
The term also refers to the general societal trend in Japan of infantilization and people staying in their rooms all day relying on parents for support. Hikikomori ends badly after the parent or provider dies. The dependent adult has few real life skills and no means to make money. Suicide and/or murder after the death of parents is relatively common. An estimated half a million young Japanese are extreme hermits dependent on parents (see Demographics#Japan). The English equivalent term is Peter-pan generation.