re: How do you "borrow" someone's stock share and sell it?

So, question about the short contracts...do those that hold them have to hold onto them for the duration, or can they "cash out" (or whatever the correct term is) any time they want?

In other words, can you buy one of these contracts for say...a month...and if the stock dips enough in that month for you to be happy with the profit...just go ahead and close it out early? Or do you have to wait?