What does it mean to have a 'long' or 'short' position?

LONG POSITION: 

The buying of a stock, commodity, or currency involves the expectation that the asset will increase in value. If a trader enters a trade expecting the market to drive the price of a currency pair upward, this is known as taking a long position. Similarly, some trading platforms feature a button marked “Buy”, while others may have a trade entry button labeled “Long”.

SHORT POSITION: 

The sale of a borrowed security, commodity, or currency is conducted with the expectation that the asset will decrease in value. For example, when the price moves down, it is possible to sell the base currency, such as the GBP, in GBP/USD. If the dollar gains strength, indicating that sellers (bears) are overpowering buyers (bulls), the price is observed to decrease. Traders often use the terms “Sell” and “Short” interchangeably. Similarly, some trading platforms may feature a trade entry button marked “Sell”, while another might have one labeled  “Short”.