Ok people! Here are some terms that are frequently used in fanfictions.
Well, I am not an expert. These are just what I am understood by reading other fanfics. If there's any error, feel free to send an e-mail to correct me.
1 - Heero Yuy
2 - Duo Maxwell
3 - Trowa Barton
4 - Quatre Winner
5 - Chang Wufei
6 - Zechs Merquise/Milliardo Peacecraft
9 - Noin Lucrezia
13 - Treize Khushrenada
D - Dorothy Catalonia
R - Relena Peacecraft
Aishiteru - I Love You
Angst - Sad/agony
AU - Alternate universe
Arigato - Thank you
Baka - Idiot
Daijoubu - Ok/All right
Dare - Who
Demo - But
Doushite/Nanze - Why
Gomen/Gomen nasai - Sorry
Hai - Yes
Hentai - Pervert
Honto - Really
Iie - No
Itai - Ouch
Kami - God
Kawaii - Cute
K'so - Damn!
Konnichiwa - Hello
Koi - (short for koibito) Lover
Kudasai - Please
Ja ne - See ya
Lemon - Graphic sex
Lime - Not graphic sex
Masaka - Impossible
Minna - Everyone
Nani - What?
NCS - Non censenual sex AKA rape.
Ninmu Ryoukai - Mission Acknowledged
Ninmu Kanryou - Mission Accomplished
Ohayo - Good morning
Oi - Hey
Omae o korosu - I will kill you
Onegai - Please
Onna - Woman
PWP - Plot? What plot?
POV - Point of View
Shimatta - Damn it
Shinigami - God of Death
Wo ai ni - I Love You (Chinese)
Yaoi - male x male
Yuri - female x female