From the literal translation of the word toku, meaning "house. In Japan, Otaku means somebody with an obsession. From anime, manga, vedeo games, computers, to things from train sets, stamps, spoons, ect.
In the 8o's, Otaku was used for a Japanese case where an obsessed fan murdered a voice actress for not sounding th way he invisioned his favorite character.
Otakus in Japan tend to be under-weight with poor hygen and little to no life outside of their obsession, i.e. only leaving outside of their home for their care or additions to their collection of what they are obsessing over. Thus, having their society look down upon them.
In the U.S., fans of anime and manga tend to mix up Otaku for "guru", or master. A large amount of the fans of products of Japanese entertainment tend to view Otaku as a good thing. Otaku, in the West, normally means "fan of anime/manga/video-games".
The "otakus" of the US. tend to be over-weight, have poor hygen, and have little to no life outside of their own obsession.
People in the U.S. tend to make jokes about "otakus" and their Western version of "Comic-Book Junkie" to live in their parent's basement while obsessing with their collectables.
I am such an otaku because I love manga's and Kishimoto-chan!
Yuu only leaves his house in order to get a new train set... He must be an otaku.
The Otaku had murdered the voice actress because he did not like her portrayl of his favorite character.