It can be have several meaning depending on how it is used.
It is commonly used to describe someone with an Unhealthy obsession with Japan and Japanese culture. They can sometimes be refered to as Japanophiles or weeabos.
It can also be used to describe some who is half caucasian and Japanese.
Although more commonly they are used to describe the ones with an unhealthy obsession. You know its an unhealthy obsession when you refuse to watch tv that is not of Japanese origin or in Japanese. Refuse to read something that is not or Japanese origin. Refuse to listen to music that is not J-pop etc. Refusing to do anything not related to Japanese culture.
They can be found almost anywhere. They are commonly found in anime conventions cosplaying as an anime character.
They can also be found slaughtering the language. Usually stringing random Japanese words in an english sentence.
They are often looked down upon for slaughtering the language and culture.
Most wapanese will only know the words "baka" "Kawaii" and "desu"
Most wapanese know very little about Japanese culture.
Yes Wapanese, there is more to the culture than manga, anime and sushi.