The forex market is bi-directional, meaning that you can trade both ways. You can buy or sell depending on your strategy. ‘Long’ means to buy, and you will go long when you are looking for prices to appreciate, or rise. If you are going ‘short’ you are selling because you are looking for prices to fall. Going short is just as common in currency trading as going long. If you are ‘square’ or ‘flat’, it means that your buy positions exactly offset your sell positions, or that you have no positions in the market at all.