In the context of forex, a position refers to the exposure that a trader has to a particular currency or financial instrument. A trader can either hold a long position, where they have bought a currency or instrument in the expectation that its value will increase, or a short position, where they have sold it in the expectation that its value will decrease. The size of a position is measured in lots and the profits or losses are determined by the change in value of the currency or instrument being traded.