What does it mean to go long or short?
To go long means to buy a market. To go short means to sell a market. If an investor goes long USD/JPY, he buys the USD and sells the JPY. Buying a currency means that you go long with this position. An investor takes a long position in a currency if they think it will climb. If an investor goes short USD/JPY they sell the USD and buy the JPY. An investor will go short in currency if it thinks that it is set to fall.