Well, a Fujoshi is a woman who likes manga with a homosexual male theme. A Fujoshi is almost like an Otaku, many Otakus are considered Fujoshi and the difference between them is forgotten.
The reality is that Otaku means being a fan of something, so if you’re Fujoshi you are an Otaku, but it doesn’t mean it’s the same the other way around. Anyway, they are almost synonymous in Japan and if you ask what a Fujoshi is, the answer will be a female Otaku.
The problem is that if you’re a female Otaku and you are not into that kind of theme, you might not find it very funny to be called a Fujoshi.
The movie “How to date an Otaku girl” tells the story about a Fujoshi (here, they are synonyms as the title describes it as Otaku), and shows the protagonist imagining certain scenes with her favourite male characters and her boyfriend or best friend.
One particular scene shows two singers who carry this theme and how the fans fantasize about them.
Manga and anime of this type are called B-Love that means love between boys. The industry has found a market in this and has created bands, series and games for the fans of this genre.
Finally let’s analyze the word Fujoshi:
Fujoshi =Respectable woman
Yes, the difference lies in the kanji, because the pronunciation is the same.
腐 女子 =Rotten girl
妇女 子 = Respectable woman.
Below a video of a group that carries this theme, and are called Fudan Juku.