A a common acronym, or word that is used in blogs or forums, but not quite on too many social networking sites or aim.
Usually used to shorten a comment that would normally take too long, and they're a lot easier to use, especially since the phrase the acronym is for is stated often.
Sally763: ngl i dnw Jesse's hat.
KinKin54R: lol uhuhh you will not use blogisms on AIM!
NGL = not gonna lie
mte = my thoughts exactly
iawtc = i agree with this comment
ftw = for the win
Kobe Bryant, ftw!
OMG WTF FTW!