What does it mean to cover shorts? Is that a gamble on the market going up or down?
To "short" is to bet on the market going down. To do so, you borrow a share from a trading company that owns that share, with the agreement to provide them with another share. You then sell that share.
To "cover" the short is to buy the corresponding share that you will use to pay back your trading company.
So if the value of a stock is $1000, but I predict it will go down, I will borrow a stock (not paying for it), and sell the stock for $1000.
When the market is at $800, I may then buy another stock, and use that to pay back the loan, thus covering my debt, and making $200.
If, however, after selling at $1000, if the price goes up to $1100, and the term of the loan expires, I must buy one at $1100, thus loosing $100.
In my understanding, "naked" shorts are where someone sells a stock they don't actually have (even a borrowed stock), with the intent of buying one later. These "Naked" shorts, when possible, can be used as an attack on the share value of a company, to bankrupt the company, and negatively affect the economy to which it belongs. This is part of why naked shorts are so often illegal or highly restricted... besides the inherently fraudulent nature of the transaction.