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

If you are buying a currency or an instrument, you are considered in a ‘long’ position. If you are selling on the other hand, then you are in a ‘short’ position.

For example, if you buy 1 lot of AUD/USD, this means you open a long position for 100,000 of AUD against USD. If you sell 1 lot of USD/GBP this means you open a short position for 100,000 of USD against GBP.