Short sellers borrow stock, sell it with the expectation that the stock price will drop so they can buy it back at a lower price so they can return the borrowed stock. The difference between the price they sold the shares and bought back is their profit.
For example lets say the borrow and sell 10,000 shares for $500. The price drops and they buy it back for $400 so the difference is $100 and their profit is $100 X 10,000 = $1,000,000.
Naked shorting is selling shares that you never borrowed so when the entity you sold them to needs the shares because the want to sell them or perhaps NWBO gets bought our so they need to surrender the shares their are no shares to give them so it is a Fail to Deliver. I imagine they can go for long periods of time without having to produce shares but I suspect that when the price starts to rocket higher and it looks like it is going to remain much higher you may have buyers wanting their shares if there are none it is a Fail To Deliver.
. . .. SO that is my understanding baparks but I am an engineer not a financial specialist so I encourage anyone with expertise in this area to correct me.