It could be an acronym for state income tax witholding, but more likely some text speak that the person who texted you made up.
Food For Thought
Naa stands for "nothing at all".
facebook.com/mynameisbellathorne
State Income Tax Withholding
BWT is short for about Example i've just txt her bwt it
For The Loss
is
What I wore
hmft
When you see txt/IM, that means text or instant message.
Especially in the younger generation.
FTW is an acronym that stands for "For the Win." It used to mean, "F*ck the world," but that meaning is becoming less and less popular.