I was surprised at a wrong definition of Otaku listed on Urban Dictionary.com…
Otaku is defined in the Urban Dictionary as follows:
Otaku is the honorific word of Taku (home). Otaku is extremely negative in meaning as it is used to refer to someone who stays at home all the time and doesn’t have a life (no social life, no love life, etc). Usually an otaku person has nothing better to do with their life so they pass the time by watching anime, playing videogames, surfing the internet (otaku is also used to refer to a nerd/hacker/programmer). (death_to_all, 2003)
Then I finally realize why some American people couldn’t tell the difference between Otaku and Hikikomori.
Wikipedia listed more appropriate definition as follows:
In modern Japanese slang, the term otaku refers to a fan of any particular theme, topic, or hobby. Common uses are anime otaku (a fan of anime), cosplay otaku and manga otaku (a fan of Japanese graphic novels), pasokon otaku (personal computer geeks), gÄ“mu otaku (playing video games), and wota (pronounced ‘ota’, previously referred to as “idol otaku”) that are extreme fans of idols, heavily promoted singing girls. There are also tetsudÅ otaku or denshamania (railfans) or gunji otaku (military geeks).
So, English translation could be maniac or mania. Otaku people have a specific and profound interest in something and they can interact with other fans in person and online even though they talk and act in a geeky way. Otaku can be used positively to express their expertise.
On the other hand, Hikikomori people have sever difficulty in social interaction so that they stay at home all the time, have nothing better to do with their life, and pass the time by watching anime, playing videogames and surfing the internet as Urban Dictionary explains about Otaku people. I don’t know how this misinterpretation started but it might be attributed to the honorific word of Taku (home) since the image of being at home can be connected the word, Taku.
The meaning of new terms created in popular culture is always changing and hard to define. While researchers have hard time to keep up with changes, the participatory culture like Wikipedia can take more prompt action about popular culture.