I learned about this phenomenon through this article:
"Why won't 541,000 young Japanese leave the house?" (Emiko Jozuka, CNN, 9/12/16):
According to a Japanese cabinet survey released Wednesday, there are currently 541,000 young Japanese aged between 15 and 39 who lead similarly reclusive lives.
These people are known as hikikomori — a term the Japanese Health, Labor and Welfare Ministry uses to define those who haven't left their homes or interacted with others for at least six months.
The term was coined as early as the 1980s, but there is still much debate on how exactly this condition is triggered and how it can be defined.
Somehow or other, I found both the sound and the meaning of this word to be intensely beguiling.
I think that the most common way of writing the term is this mixture of one kanji and four hiragana: hikikomori 引きこもり. But it can also be written in at least nine other ways: 引き篭もり, 引き篭り, 引き籠もり, 引き籠り, 引篭もり, 引篭り, 引籠もり, 引籠り, ヒキコモリ, all with the same pronunciation
The verb hiku 引く by itself means "draw, pull", and komoru 篭/籠もる means "seclude oneself".
Now for definitions of the word.
From the online jisho dictionary:
2. social withdrawal; shunning other people
There's also the slang, derogatory derivate, hikkii ヒッキー: n. someone who withdraws from society (e.g. hides in their room) < hikikomori (from tangorin).
It's clear that the hikikomori phenomenon is not new, and is quite well documented. Variously described in English as "asociality" and "(acute) social withdrawal," it's the subject of both scholarly and public attention.
In sum, hikikomori has been a major social issue recently in Japan, apparently more so than 10-15 years ago, though it already existed then and has been listed as a loan-word in the Oxford English Dictionary since 2010.
I once (more than twenty years ago) met a young Japanese man in his early twenties who had been sent by his parents to China simply to live in seclusion in a room that they had rented for him for years. It was in a university dorm in Sichuan, though he wasn't a student at the university, because he was incapable of going to classes. He stayed in his room nearly all the time year after year. And what a mess it was! Manga everywhere! Games all over the place. He couldn't communicate with the Chinese students either. He must have been a hikikomori, though I don't remember if anybody called him that.
[h.t. John Rohsenow; thanks to Nathan Hopson, Miki Morita, and Hiroko Sherry]