Otaku means...a nerd, a geek, a freak....we, Japanese, only use this term when we are making fun of those people who are indoors, hate to socialize, and love to hang out by himself by studying, playing games, reading mangas, collecting anime toys... I discussed about this topic lots of times with Ryo when I saw him first time, because it really doesn't sound good to us.
Mostly Otaku is term for male, because those actions take place among guys in Japan. So girls often say "kyaaa, he is so 'Ottakkiiiiiiiiiiiii'!!!"- like English way of saying "man, he is so fuckin gay"
Otaku comes from a word "house"- so meaning "indoor boy"
The image of a Otaku boy which Japanese Manga creaters draw is: a boy with glasses, in a dark room, one desktop light and a bit of smile when he is making anime toys.
Perhaps, if you are looking for a word which describes people who loves manga and games with passion, we must have a different word for that, but I don't come up anything at the moment, because I went to clubbin last night and danced too much with drinks... :lol: