if they say lemon, or any citrus fruits, it usually means smut. Not sure how it got there, urban dictionary might know *shrugs*
Citrus is a way to refer to fruit such as lemons, oranges, grapefruit. So I imagine the taste that the fanfiction leaves in the mouth is similar.
Lol wtf is this? I asked for the meaning of citrus in fanfic. Not a yuri manga/anime list too bad i'm not into yuri