In forex trading we can trade USD currency in pair like GBPUSD, EURUSD, USDJPY and more, usually when USD strengthening to another currency will occurs in all currency, however average price move can be vary, and not always working like that. So when trading USD we also need to understand character of each pairs, included average movement, volatility also the market behaviour.
One advantage trading USD pair usually has low spread, like EURUSD in FXOpen start with 0.0 spread even possible get negative spread.