(part of common anime words)
To begin with, the way the word's used, a fujoshi 腐女子 is a girl who's fanatical for yaoi やおい.
Great... but what is yaoi? Well, yaoi is homo-erotic fiction, that is, a word for gay porn found in manga, anime, games, light novels, etc. It stands for YAma nashi, Ochi nashi, Imi nashi 山なし、落ちなし、意味なし, literally "no climax, no fall, no meaning." Which is an overly complicated way to say "instead of building a gay romance story, cut straight to the chase."
So there you have it, fujoshi are girls who like gay porn drawings. It's a label, like otaku オタク or hikikomori 引きこもり. But it's a little different from tsundere ツンデレ, as fujoshi is used mainly for real people and not for characters.
Fujoshi 腐女子 in Japanese
Alright, but what about the actual meaning of fujoshi in Japanese? Like, what does the word fujoshi means in the Japanese language literally, and not how it's used?
Well, in that case, fujoshi means "rotten girl." The word joshi 女子 means "girl" in Japanese, joining the kanji for woman 女 and child 子. The last kanji, 腐, means "rotten," as it can be seen in the verb kusaru 腐る, which means "to rot."
But what does "rotten girl" or perhaps "rotting girl" have to do with yaoi? Putting it in a simple way, yaoi is indecent. It's porn, after all. So fujoshi aren't your sincere beacon of decency joshi, they are your rotten descending into depravity fujoshi.
(character Oshiroi Hana 白粉花 from the anime Ben-To ベン・トー is a fujoshi)
Like I said, the joshi 女子 in fujoshi means "girl" so it's not a coincidence that the word fujoshi is used only to talk about girls who are into yaoi and never guys who are into yaoi. Then again, just call those guys gay or whatever, there is no need to make a new word just for them.
Or is there?
The word fudanshi is technically fujoshi counterpart. The danshi 男子 part has the kanji for man 男 instead of woman 女 and it stands for "boy" instead of girl. So fudanshi is literally "rotten boy". And yes, fudanshi is used for guys who are into yaoi just like fujoshi is used for girls.
But why? Why not just call them gay?!?! Why a new word?!
Technically, neither fudanshi nor fujoshi are about gay porn. They are about yaoi, gay porn fiction. So even though 99,9% of the fudanshi are probably gay there is always the possibility of that one weird one who is totally not gay and reads yaoi while muttering to himself "no homo."
In the Japanese fiction industry fujoshi are considered a niche market. They are what you get when you make yaoi works that are targeted at shoujo 少女 or josei 女性 demographics.
That is, it's different to produce gay cartoon porn for girls (fujoshi) vs. making gay cartoon porn for guys (fudanshi), just like shounen and shoujo manga are produced differently. So you can expect plenty of bishounen 美少年 in fujoshi-targeted yaoi, and for fudanshi-targeted yaoi plenty of... plenty of... I don't know. Something else.
The point is that for many anime with male characters (that is most of them) you can find fujoshi merchandising, officially endorsed fujoshi products, like character pillows (dakimakura 抱きまくら), not to mention unofficial fujoshi doujinshi 同人誌, etc.
What is Fujobait
Closing the topics we started with, let's talk about fujobait. It's not a Japanese word, it's an English word obviously joining fujoshi with bait. A bait for fujoshi, for the fujoshi audience.
An anime (manga, etc.) with fujobait is an anime which has unusually pretty male characters, bishounen 美少年, and slaps homo-romantic / Boys' Love-esque scenes around for no reason, thereby creating a habitat for fujoshi to proliferate.
These fujobait things are forced, obviously. They are fujoshi fanservice. That means these anime are as bad as your usual anime with forced fanservice, only it caters to a niche audience, the fujoshi.
Why Fujobait Exists
Money, of course! If you make an yaoi anime you're out of money, because you're essentially porn and won't show on any good TV slot. Make a BL anime you get a half-ass TV slot at best, but the audience that is not into BL will never watch it.
So your best bet is making the most generic anime possible that won't scare your public away. But just because aren't scaring them away doesn't mean you're hooking them in either. Now your anime is generic and nobody will talk about it!
But then there was a devious plan. What if you made your male characters so pretty fujoshi would notice but the rest of the audience wouldn't mind or just find it funny. And then include some gay jokes in the middle that fujoshi would definitely notice but the audience would just laugh about?
That would be perfect! Now you have an anime that is popular with a niche audience and that can be watched by everyone! There is only one problem, though.
Fujobait anime are generally shit and everyone despises them as much as fanservice-filled anime.