Basically, a lemon story is an erotic story, including romantic and sexual situations. But, most of the time, it's about sexual scenes or content. Obviously, lemon stories are for major readers, but alot of minors still read them (take for example myself). So, if you're minor, you better read them while mommy and daddy are not around.
Each lemon author has his/her own style and way to write his/her stories. You can often see "Yaoï" lemons (yaoï means male/male erotic story). In these cases, there are two important kinds of Yaoï: Soft and Hard. You may be one of these people who enjoys to read a cute male/male story. So, it's preferable to find a Soft Yaoï. For those who prefer something harder (and maybe disgusting for alot of people), you better choose a Hard Yaoï.
There's a special japanese therm for female/male lemons, but I don't remember it. Female/Male lemons are most common. I think it's more natural to write sexual situations about a boy and a girl. You can also find Female/Female lemons. These are like Yaoï. Like I said, it may be digusting for you, but some other people may enjoy these kinds of story.
Then, there are the most uncommon and bizarre lemons: Human/Animal, or Human/Monster. I won't say anything bad about these kinds of lemon because I'm quite open about lemon, but I have to say that they are not really popular, even though people can like them. For myself, I don't really mind, as long as it's well written.
I won't talk about my three different kind of lemon in this section, but in the Archive section. So, I hope you know a little more about lemon and the next time you'll see this word, you'll know what it is about.
If you have any question, suggestion or comment, please, feel free to e-mail me at danielle_fireseed@hotmail.com