Speaking of SHORTS......I thought it was not allowed to short...

Speaking of SHORTS......I thought it was not allowed to short stocks on the ASX.? Is that true? OR is it for only the Australian investors?
It seems unfair that some funds or traders from other countries can do it?

I really don't get the whole "SHORTING A STOCK THING"....can someone give me a quick explanation pls?
I know I can't short any stock using Commsec....not that I've tried, Its just that their is a confirm statement that you are not trying to sell a stock you don't own.