LONG POSITION: 

The buying of a security such as stock, commodity, or currency, with the expectation that the asset will rise in value. If a trader is in a trade on the basis that the market is going to force the price of a currency pair upward this is known as a long position. Similarly, as a button marked "Buy", where another might have a trade entry button marked "Long".

SHORT POSITION: 

The sale of a borrowed security, commodity, or currency with the expectation that the asset will fall in value. In another hand, when the price moves down, it is possible to sell the base currency (i.e. the GBP in GBP/USD). When the dollar gains strength (i.e. the bear - sellers - starts to get the upper hand of the bull - buyers), the price will be seen to move down. Traders will often use the terms sell and short interchangeably. Similarly, the software will have a trade entry button marked "Sell", where another might have a trade entry button marked "Short".