Otaku is a Japanese word that has taken on a new meaning lately. It’s taken on an even newer meaning in the U.S. Let me explain.
Otaku is a Japanese word that means "me" or "I" in a deferential way. Basically, it’s a way of talking about yourself in the third person. Talking about yourself in the third person is not something we really do in English but when you study Japanese you’ll see that Japanese sometimes does its grammar different than English. Suffice it to say that if you use the word, you're being humble. A few years back you could hear women, especially housewives, talking about themselves with the word "otaku" all the time.
Otaku took on a newer meaning in Japan not too long ago. Guys who were real anime fanatics were usually pretty meek, geeky guys. I’m talking about the guys who wear thick glasses and keep to themselves. I know, I know, it sounds stereotypical, but there is something to this. The guys who were real hardcore anime/manga lover were most often geeky guys. These shy, soft spoken guys would spend a lot of their money on anime, manga, and related stuff and spend a lot of time going to cons, drawing their own comics, etc. These guys sometimes got so shy that they took on ways of speaking that were feminine. Some of these shy fanboys started referring to themselves with the word "otaku", which is pretty much a no-no for a guy in Japan.
After a news story swept Japan about an anime fan who murdered someone a lot of people were upset. Media hype in the following weeks put anime fans in a poor light (in Japan). Hardcore anime fans started being called "otakus" and the word took on a negative connotation. An otaku was now a socially maladjusted young man who spent all his time with his hobbies and not enough time with real people.
Over time a bit of the edge was taken off the term and otaku came to mean anyone who spent too much time and money on their hobbies. Generally it isn’t the greatest thing to be called an otaku in Japan.
Among anime fans in the U.S. the word otaku has come to mean anyone who likes Japanese anime and/or manga. At anime conventions in the U.S. I've heard stuff like this countless times:
"Are you an otaku?" "Yeah, I like anime."
My Chinese friends in California and I meet up every summer and joke about it. We agree I’m a mecha otaku because I’ve spent hundreds upon hundreds of dollars collecting mecha artbooks. 2 of my friends are computer otakus because they both spend ridiculous amounts of money making their bedrooms look like electronic stores. One of us, a short guy who I swear lives with a frown carved into his face, is a just plain "otaku." My friends and I all agree he’s the closest to the Japanese meaning of "otaku" that we’ve ever seen. He lives at home, spends ALL his money on anime stuff and knows the most obscure facts about anime. We won’t go into his room but we like having him around.