Which means that they need to "cover" their bet, by effectively selling back their position - at a loss, but at a smaller loss than if the price movement that caused the loss continued.

"short positions" are positions where the player has sold the asset (usually by borrowing it before, or via equivalent instruments), ie is betting on the price going down (the expectation is to be able to buy back the asset later for less).

I'm not sure exactly how "open interest" is defined, but I would imagine it's the number of offers officially put up on the market to buy a given asset at prices that are currently above market price (and are thus unfulfilled): for instance, if you give an order to your broker to buy 1,000 barrels at $150.

In the long run, we're all dead. John Maynard Keynes