FFA (also f-fa and variants): Fail Fandom Anon, the anonmeme you've been looking at.

• Nonny, nonnie, anon = the people posting comments on meme
• AYRT = anon you replied to
• AIRT = anon I'm replying 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)
• DA = different anon (possibly new to the subthread, may already be contributing to the discussion in a different subthread)
• 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 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.
• ASOIAF = see GoT.
• AFFN, AFF.net, variants = AdultFanFiction.net.
• 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 =
  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).
• 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 = Avatar: The Last Airbender.
• AU = Alternate Universe.
• B5 = Babylon 5.
• BaTB = Beauty and the Beast, typically the Disney renaissance movie.
• 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.
• BNF = Big Name Fan.
• BL = boys' love.
• BOFQ = Bitter Old Fandom Queen.
• 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 Bangtan Boys.
• BtVS = 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.
• CSI = The Crime Scene Investigation TV series.
• 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 = Detroit: Become Human.
• DBZ = Dragon Ball Z.
• DCU - DC (Comics) Cinematic Universe.
• DD = “Details, details!” A call for evasive/coy nonnies to spill the beans about whatever.
• DDLC = 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 = How I Met Your Mother.
• HPMOR = “Harry Potter and the Methods of Rationality,” a smug longfic by “rationalist” cultist Eliezer Yudkowsky.
• HTGAWM = How to Get Away with Murder.
• HTP = HYDRA Trash Party
• IASIP = It's Always Sunny in Philadelphia.
• ITT = in this thread.
• JGY = Jin Guang Yao, a character in The Untamed. Sometimes pronounced “Jiggy” by Western fans.
• JS&MN = Jonathan Strange and Mr. Norrell.
• LJ = LiveJournal.
• LJW = Lan Wangji, a character in The Untamed.
• 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/
• 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.
• 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.
• MSF = Migratory Slash Fan[dom]. Refers to fandoms transiently popular with certain, particularly big-name slash fans, often with white-cock juggernaut pairings.
• NFHA = Nathan Fillion Hating Anon.
• NN = author Naomi Novik aka BNF Astolat, cofounder of OTW. Formerly, often referred to 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, there's no reason not to do so.
• NNF = No Name Fan. Very rarely also LNF, Little/Low Name Fan.
• NOTP = opposite of an OTP.
• OAA = Overly Aggressive Anon.
• OFC = Original Female Character.
• OEA = Overly Earnest Anon.
• OLA = Overly Literal Anon.
• OSA = Overly Sensitive Anon.
• OMC = Original Male Character.
• OMGCP = “Oh My God Check Please,” created because “CP” is unfortunately ambiguous.
• OMD = Original Male Dog.
• 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.
• 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 = Pirates of the Caribbean.
• PotO = Phantom of the Opera.
• PWP = Porn Without Plot, also known as “Plot? What Plot?”
• QAF = Queer as Folk.
• 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.
• SGA = Stargate Atlantis.
• 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, popular manga/anime series
• SPN = Supernatural.
• SRB = Sarah Rees Brennan, pro author who came from fandom. Friend of Cassie Claire and frequently wanky in her own right.
• STID, ST:ID = Not in fact a sexually transmitted ailment, 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's Official 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.
• 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.
  2. Torchwood.
  3. Trigger warning. Depends on context.
• TWS = see CA:TWS.
• TWW = The West Wing.
• TYWAU = Things You Wouldn't Admit Unanon. One of the common threads on the meme, usually on the first page. Occasionally rendered as “TYWNAU.”
• UST = unresolved sexual tension.
• WF = Winterfox.
• WKX = Wen Ke Xing, a character in Word of Honor/Faraway Wanderers.
• WNGWJLEO = We're Not Gay, We Just Love Each Other.
• 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 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 Zi Shu, a character in Word of Honor/Faraway Wanderers.

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