Long is a position that profits when the price of an instrument rises. Going long means buying an instrument in the expectation of selling it higher later.
You can go long in stocks, forex, commodities, indices, futures, options, and CFDs. In forex, going long on a pair means buying the base currency and selling the quote currency.
Long is the opposite of short, and different again from flat. A long trader expects prices to rise; a short trader expects them to fall; a flat trader holds no position and has no exposure either way. Traders manage long-position risk with stop-loss orders, position sizing, and set exit levels.
You expect gold to rise from USD 2,350 to USD 2,380.
You open a long position on XAUUSD at USD 2,350.
If XAUUSD rises to USD 2,380, you can close for a profit of USD 30 per unit. If it falls instead, the long position loses value.
USD 2,380 - USD 2,350 = USD 30