What is Otaku?

Otaku (おたく/オタク^?) is a Japanese term used to refer to people with obsessive interests, particularly (but not limited to) anime andmanga. The exact origin of the term is unknown with various research books discussing the topic, noting the terms existence since the 1970s and the first published usage in the Macross anime in 1982. In Japan, otaku is a broad and largely negative term to define the obsessive interests of any type. The negativity stemming from the reporting on Tsutomu Miyazaki's as "The Otaku Murder" in 1989 and the media incorrectly identifying another murder, Kaoru Kobayashi, as an otaku. English usage of the term refers to an obsessive interest in anime and manga, but lacks the stigma of its Japanese usage.

from  : http://en.wikipedia.org/wiki/Otaku