I'm new to the DC universe and I saw someone post the Smoke cloud is the defense for HSS.

Can someone tell me how that is?

HSS does not allow you to ignore hindering terrain, so Smoke Cloud would stop the Flash cold in his tracks.

Of course, it won't affect Supes, because he flys.

Ok so even though you don't have to stop when you move adjacent to a character he has to stop for a chair?

Yes, you are correct - Flash could trip on the chair, or embed the smoke particles in his skin if he goes to fast...but Brainiac - no problem.

HSS ignores the efect of breakway, but does not ignore the effect of hindering terrain. Flash could run in circles around the Smoke Cloud or chair, as well as Brainiac. However, if he enters a square with either smoke cloud or a chair, his movement comes to an end. As for Brainiac, Flash can't enter the same square as Brainiac. HSS does not allow a piece to exist in the same square as another piece.

The defense that smoke cloud could provide would be too either completely surround a figure with smoke cloud or to lay the cloud in such a way that the HSS fig couldn't make an attack and get away.

At least, that's my take on it.