RT = Retweet. See @hellowahab‘s post on Twitter Acronyms .
PRT = Partial Retweet / Please Retweet. PRT means the RT’ed tweet has been edited, usually to fit a username within the character limit.
OH = Overheard. ‘OH’ is commonly used at conferences or while traveling. OH indicates a quotation of someone else’s remarks.
DM = Direct Message. DMs are Twitter’s email. “DM me” means take the discussion private.
@ = Reply to [username]. @ can also be used expressing ‘at,’ as in location.
BTW = By The Way. BTW is an easy way to add an aside. It’s Twitter’s version of a segue.
FTW = For The Win. Whatever the action or product FTW modifies is *good*.
FTL = For The Loss (or For The Lose). FTL is generally an expression of disappointment, disapproval or dismay. It’s the opposite of FTW.
IRL = In Real Life. What’s true on Twitter may not be true IRL.
FTF = Face to Face. FTF or F2F refers to an actual meeting in person, IRL.
IMHO = In My Honest Opinion. IMHO usually indicates that ‘This is an op-ed tweet, not a factual assertion.
YMMV = Your Mileage May Vary. In other words (IOW), what’s true in my experience (IMX) may differ from yours if you try.
BR = Best Regards. BR is a useful way of being cordial, particularly when making a
difficult request, submitting a complaint, or when introducing yourself.
b/c = because.
JV = Joint Venture. A JV refers to a collaborative enterprise between Twitterers on a project.
LMK = Let Me Know. Tweet me back (TMB) when you have more information about a question or a decision on a request.
ROFL = Rolling On the Floor Laughing
Mostly copied and edited from:- http://pistachioconsulting.com/top-15-twitter-acronyms/