What does it mean if one prong from our three pronged dryer plug has a burn mark and was smelling?

Either the prong, and/or the jaws inside the plug, had loosen, causing heat.

Both the receptacle and plug needs to be changed.

We noticed a smell coming from dryer and unplugged it. One prong from three pronged plug has large burn mark on it.

Weak or loose connection, I would replace the receptacle and Dryer Cord.
Loose connections generate heat.

Please do not start new threads for same question, Merged

Many times the plug blade can be sanded with 400 grit sandpaper, but the outlet MUST be replaced.

I somehow didn't read TK's and duplicated what he said?

It's a merged thread. So Tk and you said the same thing at different times without seeing tk's response.

There is usually always some confusion with merged threads.