FFA (also f-fa and variants): Fail Fandom Anon.

• Nonny, nonnie, anon = the people posting comments on meme.
• AYRT = anon you replied to.
• AIRT = anon I'm replying/I replied to.
• A AIRT RT = anon [whom] the anon I'm replying to [earlier] replied to (usually the anon two comments up instead of one).
• AVRT = anon velociraptor replied to.
• NAYRT = not the anon you replied to.
• SA = same anon (when you're adding to or correcting something in a comment you just submitted).
• NA = new anon (not previously part of the discussion).
• NNA = new new anon (to distinguish oneself from the NA one just replied to). Not frequently used.
• DDA = different different anon (to distinguish oneself from the DA one just replied to). Not frequently used.
• NNA = new new anon (to distinguish oneself from the NA one just replied to). Not frequently used.
• OP = original poster (person who started the thread).
• SubOP = subthread OP.
• YADA = yet another different anon.
• YANA = yet another new anon (when it doesn't mean You Are Not Alone).

• 2ha = the Chinese novel The Husky and His White Cat Shizun.
• A/B/O = Alpha/Beta/Omega[verse] fic or characters. See Dogfuck Rapeworld (or the Fanlore page) for details.
• AFFN, AFF.net, variants = AdultFanFiction.net.
• AHEW = “All He Ever Wanted,” a Hetalia: Axis Powers fanfic.
• AITA = Am I The Asshole? Based on the subreddit of the same name.
• ANH = Star Wars: A New Hope.
• AO3 = Archive of Our Own, a fanfiction archive created/maintained by the OTW.
• AOS, AoS =
  1. “Alternate Original Series” (Star Trek reboot movies).
  2. TV series Marvel's Agents of S.H.I.E.L.D.
  3. Age of Sail (canons such as Horatio Hornblower or Patrick O'Brian's Aubrey/Maturin).
• ASOIAF, ASoIaF = see GoT.
• ATG = Any Two Guys, more rarely Any Two Girls. In reference to fic with generic characterization; the pairing could be “any two guys.” Used in "Guess the ATG" game threads (beloved of nonnies for the creative name-swapping possibilities).
• ATLA, AtLA = the Western cartoon series Avatar: The Last Airbender.
• AU = Alternate Universe.
• B5 = Babylon 5.
• BatB, BATB = Beauty and the Beast, typically the 1991 Disney remake, sometimes the 2017 film.
• BEC = (Look at That) Bitch Eating Crackers, referring to a grudge that makes the bearer annoyed by even the most innocuous actions of the target.
• BFE = Bangs, Fests, Exchanges - one of meme's common threads.
• BL = boys' love.
• BNF = Big Name Fan.
• BOFQ = Bitter Old Fandom Queen. Not used very much anymore.
• BOTW, BoTW = Legend of Zelda: Breath of the Wild.
• BS = Benjanun Sriduangkaew, the pro-writing pseudonym of Winterfox.
• BTS = a K-pop boy band, also known as the Bangtan Boys.
• BtVS = the 1990s TV series Buffy the Vampire Slayer.
• CA:TWS, TWS = Captain America: The Winter Soldier.
• CBT = on FFA, equally likely to be earnestly used in discussions about therapy options (Cognitive Behavioral Therapy) or in discussions about kink (Cock and Ball Torture).
• CC = Cassie Claire.
• CEBLA = Chris Evans' Butthole Loving Anon.
• CNTW = Choose Not to Warn.
• CQL = Chen Qing Ling/The Untamed.
• CSI = the Crime Scene Investigation TV franchise.
• CTSC = comment(ing) to see comments. No longer a thing since the move to Dreamwidth.
• DAYD = “Dumbledore's Army and the Year of Darkness,” a fanfic by Thanfiction.
• DBH = the game Detroit: Become Human.
• DBZ = the anime Dragon Ball Z.
• DCU - DC (Comics) Cinematic Universe.
• DD = “Details, details!” A call for evasive/coy nonnies to spill the beans about whatever.
• DDLC = the VN Doki Doki Literature Club.
• DNW = Do Not Want, used in fanworks exchanges to refer nonjudgmentally to things the recipient does not wish to have in their gift.
• DW = Usually either Doctor Who or Dreamwidth; depends on context.
• DFRW = Dog Fuck Rape World.
• EFRW = Eldritchfuck Roseworld, a loose multiverse of Homestuck AUs.
• EFW = existential flame war, based on the LJ comm of the same name, which originated in the Usenet group alt.callahans. Enjoyed by some, reviled by others.
• EPH = emergency pinch hit, in fanworks exchanges.
• EYM = ElfYourMother, a Dragon Age wanker.
• FE3H = Fire Emblem: Three Houses.
• FF = Final Fantasy, usually followed by a number or Roman numeral to indicate the version.
• FFN, FF.net, FF, variants = FanFiction.net.
• FMA = Full Metal Alchemist.
• FWA = Fog Warriors Anon, Dragon Age troll.
• GoT = Game of Thrones, TV series based on George R.R. Martin's A Song of Ice and Fire (ASOIAF).
• GotG = Guardians of the Galaxy.
• GRRM = George R.R. Martin, author of ASOIAF.
• GSN = Grumpy Sutcliff Nonnies.
• HIMYM = the TV series How I Met Your Mother.
• HP = the Harry Potter series of books and movies.
• HPMOR = “Harry Potter and the Methods of Rationality,” a smug longfic by “rationalist” cultist Eliezer Yudkowsky.
• HTGAWM = the TV series How to Get Away with Murder.
• HTP = HYDRA Trash Party.
• IASIP = the TV series It's Always Sunny in Philadelphia.
• ITT = in this thread.
• JGL = the actor Joseph Gordon Levitt, best known on meme for playing Arthur in the 2010 MSF movie Inception.
• JGY = Jin Guangyao, a character in the Chinese TV series CQL/The Untamed. Sometimes pronounced “Jiggy” by Western fans.
• JKR = J.K. Rowling, the author of the HP series.
• JS&MN = the novel Jonathan Strange and Mr. Norrell by Susanna Clarke.
• LJ = LiveJournal.
• LL = “Link links!” (unless you're an spnanonhaven/FFA bimemer, in which case it stands for “Leonidaslion”).
• LoK = Legend of Korra.
• LotRiPS, LOTRiPS, Lotrips = Lord of the Rings Real Person Slash.
• LWJ = Lan Wangji, a character in the Chinese TV series CQL/The Untamed.
• MCU = Marvel Cinematic Universe. Includes (at least) the Thor, Avengers, Iron Man, and Captain America movies, as well as the Agents of S.H.I.E.L.D. TV series in its continuity.
• MDZS = Mó Dào Zǔ Shī/Grandmasters of Demonic Cultivation, a Chinese novel and donghua TV series.
• MFVW/MFCW = Mantis Fuck Vore [or Consent] World, an FFA-originated offshoot of DFRW/A/B/O.
• MLP, MLP:FiM = My Little Pony: Friendship is Magic. Meme critter Pinkie Pie either hails from there or named herself after one of the characters.
• MNF = Medium Name Fan.
• MRF = Mary Renault Fics, a notoriously gatekeeping LJ community that went out in a blaze of wank.
• MSF = Migratory Slash Fan[dom]. Refers to fandoms transiently popular with certain fans, particularly slash BNFs. The juggernaut pairings are often white and male, a/k/a “whitecock.”
• NCIS = the TV series NCIS: Naval Criminal Investigative Service.
• NFHA = Nathan Fillion Hating Anon.
• NN = author Naomi Novik, a/k/a BNF Astolat, cofounder of the OTW. She was once referred to on meme solely by her initials to avoid linking her wallet name to her fannish pseud. Now that she has herself connected the two identities and also personally and publicly accepted a Hugo Award on behalf of AO3, meme rules permit “NN” and “Astolat” to be used interchangeably.
• NNF = No Name Fan. Very rarely also LNF, Little/Low Name Fan.
• NOTP = opposite of an OTP.
• OAA = Overly Aggressive Anon.
• OEA = Overly Earnest Anon.
• OFC = Original Female Character.
• OITNB = the TV show Orange is the New Black.
• OLA = Overly Literal Anon.
• OMC = Original Male Character.
• OMD = Original Male Dog.
• OMGCP = “Oh My God Check Please,” an acronym used by the Check Please fandom because “CP” is unfortunately ambiguous.
• OSA = Overly Sensitive Anon.
• OSN = Orgy Ship Nonny [page to come].
• OT3 = One True Threesome. There are also OT4s, OT5s, etc.
• OTC = One True Character.
• OTP = One True Pairing.
• OTW = Organization for Transformative Works.
• OUAT = Once Upon a Time. TV show based on fairytales, on which step-grandparent/step-grandchild incest is not intergenerational and a major pairing.
• PatB, PATB = Pinky and the Brain.
• PoA = Harry Potter and the Prisoner of Azkaban.
• POI = Person of Interest. TV show/MSF starring Michael Emerson from Lost and Jim Caviezel, a.k.a. Jesus Cavesus.
• PotC, POTC = Pirates of the Caribbean.
• PotO, POTO = Phantom of the Opera.
• PWP = Porn Without Plot, also known as “Plot? What Plot?”
• QAF = Queer as Folk.
• RDJ = the actor Robert Downey, Jr., best known on meme for playing Tony Stark in the MCU.
• RH = Requires Only That You Hate, a blog run by Winterfox.
• ROTJ = Star Wars: Return of the Jedi.
• RP = roleplay.
• RPF, RPS = Real-Person Fic, Real-Person Slash.
• SFP = Sad French People, a DW anonmeme for Les Misérables fandom that sprang from FFA and that ultimately wanked itself to death.
• SGA = Stargate Atlantis.
• SHL = Shan He Ling/Word of Honor.
• SJ, SJW = social justice, social justice warrior.
• SMOF = “Secret Master of Fandom,” an old-school fandom term referring to conrunners and similar BNFs.
• SnK/AoT = Shingeki no Kyojin/Attack on Titan, a popular manga/anime series.
• SPN = Supernatural.
• SRB = Sarah Rees Brennan, pro author who started in fandom. Friend of Cassie Claire and frequently wanky in her own right.
• STID, ST:ID = Not in fact a sexually transmitted ailment, despite its similarities to one, but Star Trek: Into Darkness (the 2013 movie, second in the ST:AOS continuity).
• ST:TNG = Star Trek: The Next Generation.
• ST:TOS = Star Trek: The Original Series.
• SVSSS = Scum Villain's Self-Saving System.
• SW: TFA = Star Wars: The Force Awakens. Often just “TFA.”
• TF = Thanfiction, sometimes also “ThatFucker.”
• TGCF = Tian Guan Ci Fu/Heaven Official's Blessing.
• THBP = Harry Potter and the The Half-Blood Prince.
• TJLC = The Johnlock Conspiracy.
• TLJ = Star Wars: The Last Jedi.
• TLOU2 = The Last of Us 2, an action/adventure game.
• TMA = The Magnus Archives, a horror podcast.
• TPTB = “The Powers That Be,” referring to showrunners and movie producers.
• TROS, TRoS = Star Wars: The Rise of Skywalker.
• TSN = On FFA, usually refers to The Social Network (2010 slashbait film), more rarely to The Sentinel (1990s slashbait TV series).
• TW =
  1. Teen Wolf (the TV show).
  2. Torchwood.
  3. Trigger warning. Depends on context.
• TWS = see CA:TWS.
• TWW = The West Wing, 1990s TV show directed by Aaron Sorkin.
• TYWAU, TYWNAU = Things You Wouldn't Admit Unanon. One of the common threads on the meme, usually on the first page.
• UST = unresolved sexual tension.
• VN = visual novel.
• w4w = warlock4warlock, or “wiffu,” another DW anonmeme, on which discussion of het ships is not allowed.
• WF = Winterfox.
• WKX = Wen Kexing, a character in in the Chinese TV series SHL/Word of Honor.
• WNGWJLEO = We're Not Gay, We Just Love Each Other.
• WoT = WankofThedas, a defunct DW anonmeme for Dragon Age fandom.
• WS = He who shall not be named, for he is a notorious self-googler and will show up to act out on meme.
• WSA = Weird Scenario Anon. Just what it says on the tin.
• WSJ = On meme, normally Weekly Shounen Jump, a major manga magazine, rather than the Wall Street Journal.
• WTNV = Welcome to Night Vale, a podcast.
• WTNVNA = Welcome to Night Vale Hating Anon, a long-time troll.
• WWX = Wei Wuxian, a character in the Chinese TV series CQL/The Untamed.
• YKINMKATOK = Your Kink Is Not My Kink And That's OK. Nonnies usually call this concept KINKTOMATO instead, as it's snappier and easier to remember.
• ZSS = Zhou Zishu, a character in the Chinese TV series SHL/Word of Honor.

(Some content cribbed from FFA's profile page. For some concepts mentioned on this page, there may be more information at Fanlore.org.)