Shorting a stock is selling shares when you don't actually own any.
When you buy a stock, you're taking a long position (not that you're holding it long-term, that's just the term). If the stock price goes up, you make money; if the stock goes to $0, you have lost all your investment.
When you short a stock, like I said, you sell shares that you don't actually own. You make money when the stock price goes down and you cover the shares (sort of like a buy - when you shorted the stock, your broker "borrowed" the shares that you sold.) If the price goes up, you're losing money. Unlike a buy, you can lose a lot more than 100% of the initial value - if the stock price triples and you sell, you've lost 3 times the money of the value when you initially shorted - that's why you read people here about shorters "covering" - they're closing the short before the price gets too high so they don't lose too much money.
JAMN is sold on the OTC market. Most US brokers don't handle short sells for OTC stocks.
Hope that helps.
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