by Bliss Hanlin, a Community Manager for eModeration
Twitter abbreviations and acronyms are an odd mash-up of text slang, old school chat room phrases, common sense short forms and corporate buzzwords.  There is nothing more terrible than parsing a customer tweet and finding out what you once thought was a compliment was really a product slam or worse, a drug reference.  (Small personal anecdote – for the longest time, I thought HAGN was some form of Scandinavian slang for good-bye.)
While not quite a comprehensive dictionary of all things Twitter.com, what follows below is a quick-print glossary of common Twitter abbreviations.  Notice one we missed?  We would love to include it and credit you for the spot.  Just leave a note for us in the comments.

image courtesy of Twittonary.com

Technical Twitter abbreviations: •    CC = Carbon-copy. Works the same way as email •    CX = Correction •    CT = Cuttweet.  Another way of saying partial retweet •    DM = Direct message. A direct-message is a message only you and the person who sent it can read •    HT = Hat tip. This is a way of attributing a link to another Twitter user •    MT = Modified tweet. This means the tweet you're looking at is a paraphrase of a tweet originally written by someone else •    PRT = Partial retweet. The tweet you're looking at is the truncated version of someone else's tweet. •    PRT = Please retweet, a plea to put at the end of a tweet •    RT = Retweet. The tweet you're looking at was forwarded to you by another user Industry Twitter abbreviations: •    EM = Email Marketing •    EZine = Electronic Magazine •    FB = Facebook •    LI = LinkedIn •    SEO = Search Engine Optimization •    SM = Social Media •    SMM = Social Media Marketing •    SMO = Social Media Optimization •    SN = Social Network •    SROI = Social Return on Investment •    UGC = User Generated Content •    YT = YouTube
Conversational abbreviations: •    # = start to a hashtag, or a way of organizing subjects on Twitter •    •    AB/ABT = About •    AFAIK = As far as I know •    AYFKMWTS = Are you f---ing kidding me with this s---? •    B4 = Before •    BFN = Bye for now •    BGD = Background •    BH = Blockhead •    BR = Best regards •    BTW = By the way •    CD9 = Code 9, parents are around •    CHK = Check •    CUL8R = See you later •    DAM = Don’t annoy me •    DD = Dear daughter •    DF = Dear fiancé •    DP = used to mean “profile pic” •    DS = Dear son •    DYK = Did you know, Do you know •    EM/EML = Email •    EMA = Email address •    F2F /FTF = Face to face •    FB = Facebook, F--- buddy •    FF = Follow Friday •    FFS = For F---‘s Sake •    FML = F--- my life. •    FOTD = Find of the day •    FTW = For the win, F--- the world •    FUBAR = F---ed up beyond all repair (slang from the US Military) •    FWIW = For what it's worth. •    GMAFB = Give me a f---ing break •    GTFOOH = Get the f--- out of here •    GTS = Guess the song •    HAGN = Have a good night •    HAND = Have a nice day •    HOTD = Headline of the day •    HT = Heard through •    HTH = Hope that helps •    IC = I see •    ICYMI = "In case you missed it," a quick way to apologize for retweeting your own material •    IDK = I don't know •    IIRC = If I remember correctly •    IMHO = In my humble opinion. •    IRL = In real life •    IWSN = I want sex now •    JK = Just kidding, joke •    JSYK = Just so you know •    JV = Joint venture •    KK = Kewl kewl, or ok, got it •    KYSO = Knock your socks off •    LHH = Laugh hella hard (stronger version of LOL) •    LMAO = Laughing my ass off •    LMK = Let me know •    LO = Little One (child) •    LOL = Laugh out loud •    MM = Music Monday •    MIRL = Meet in real life •    MRJN = Marijuana •    NBD = No big deal •    NCT = Nobody cares, though •    NFW = No f---ing way •    NJoy = Enjoy •    NSFW = Not safe for work •    NTS = Note to self •    OH = Overheard •    OMFG = Oh my f---ing God •    OOMF = One of my friends/followers •    ORLY = Oh, really? •    PLMK = Please let me know •    PNP = Party and Play (drugs and sex) •    QOTD = quote of the day •    RE = In reply to, in regards to •    RLRT = Real-life re-tweet, a close cousin to OH •    RTFM = Read the f---ing manual •    RTQ = Read the question •    SFW = Safe for work •    SMDH = Shaking my damn head, SMH, only more so •    SMH = Shaking my head •    SNAFU = Situation normal, all f---ed up (slang from the US Military) •    SO = Significant Other •    SOB = Son of a B---- •    SRS = Serious •    STFU = Shut the f--- up! •    STFW = Search the f---ing web! •    TFTF = Thanks for the follow •    TFTT = Thanks for this tweet •    TJ = Tweetjack, or joining a conversation belatedly to contribute to a tangent •    TL = Timeline •    TLDR/TL;DR  = Too long, didn’t read •    TMB = Tweet me back •    TT = Trending topic •    TY = Thank you •    TYIA = Thank you in advance •    TYT = Take your time •    TYVW = Thank you very much •    W or W/ = With •    W/E or WE = Whatever or weekend •    WTV = Whatever •    YGTR = You got that right •    YKWIM = You know what I mean •    YKYAT = You know you're addicted to •    YMMV = Your mileage may vary •    YOLO = You only live once •    YOYO = You're on your own •    YW = You're welcome •    ZOMG = OMG to the max
Common hashtags and chats: •   #BrandChat = private chat about branding •    #CMAD = Community Manager Appreciation Day •    #CMGR = Community Manger topic chat •    #FB = The user is sending this post to Facebook •    #FF = Short way of saying Follow Friday, or a recommendation that others follow the user •    #in = the user is sending this post to LinkedIn •    #LI = This user is sending this post to LinkedIn •   #LinkedInChat = For general use questions and questions about marketing/self-promotion on LinkedIn •   #Mmchat = Marketing and social media chat •   #Pinchat = a chat for maximizing Pinterest use •   #SMManners = Social media manners chat •   #SMMeasure = For discussion of analytics and mesaurement, lead by MarketWire and Syomos •   #SMOchat = Social Media Optimization chat lead by Stanzr •   #SocialChat = Social media chat lead by SocialParle. •   #SocialMedia = an all-inclusive chat for subjects big and small in the subject of Social Media

Many thanks to Business Insider, Webopedia, and the Twittonary for their excellent information that helped pave the way for this Twitter abbreviation compilation and to Mashable for the compilation of social media Twitter chats.  Looking for an explanation of Twitter terms, phrases, neologisms and slang that go beyond abbreviations?  Be sure to click through to see the awesome resources they have made available.