Smth

[Rihanna]

The shorter form of something

[PussyCat]

abbreviation for something.
When chatting with someone,this and many other abbreviations -such as btw(by the way),srsly(seriously),ty(thank you),brb(be right back),j/k(just kidding),etc...- may help your conversation preceed faster!

[Couch Potatoe]

Smth, an internet contraction for the word something.