Long position
Going long means buying an asset to profit from a rise. You make money if the price climbs above your entry, after costs.
Taking a long position is a bet on a rise. On EUR/USD, being long means buying euros against dollars: you profit if the euro strengthens. On the DAX or gold, you profit if the index or the metal goes up.
A long position opens at the ask and closes at the bid. The stop loss goes below the entry price, often under support or a recent low, and the take profit above it.
On a leveraged CFD, staying long can also cost a swap every night. Before holding a position for several days, check that cost in the symbol's specifications.