A somewhat derogatory term for a Caucasian (white) or Western person who emulates or adapts mannerisms, slang, and fashion stereotypically associated with Japan and Japanese culture, especially those relating to anime, without proper understanding of Japanese culture. In worst case scenarios, they are even willing to deny Japanese faults, including war crimes.
Following its automated substitution with a nonce word from Perry Bible Fellowship, "weeaboo" subsumed its original meaning and became the common vernacular in its place, with its dummied-down version "weeb" now being used as the common term to refer to fans of anime and manga, and correspondingly "-aboo" being adapted to refer to nutty fans of all sorts of things.
An equivalent term in Japanese is "Japan mad" (in the sense that you're mad crazy over Japan).
