Yaoi/Slash - A relationship that revolves around guys.
Shounen Ai - A term that literally means, "boys love".
Seme/Uke - Seme is the dominant figure in the relationship, while the Uke is the one who gets buttfreaked (lol).
AU - Term that means "alternate universe", or a different world/timeline than the original.
OOC - "Out of Character", or when the characters aren't acting like their usual selves.
Angst - When the fic normally has a few or a lot of depressive thoughts that can border on "here's a tissue to wipe your tears and bloe your nose" bad.
Lemon - Sex that is hugely depicted and described. This can go with a plot or PWP. Cation: Sour!
Lime - The sex is implied and/or hinted. In other words, it's not as bad as a lemon.
PWP - Porn without plot. A lot of authors also used it as Plot? What plot?
NCS - Characters get raped! AKA, non-consensual/non-con.
Fluff - Light-hearted and cute! It makes you want to just giggle and "awwww" at it.
Sap - Two love birds who contemplate (did I spell that right?) their relationship and all of that wonderful stuff. Do I even need to tell you this?