There's no difference - simply two ways to describe the mineral elements growers use to enhance plant growth.
All fertilizers contain three main ingredients (called macro-nutrients), Nitrogen(N), Phosphorus(P), and Potash(K). The three numbers on the front panel describe what percentage of each element is in the fertilizer. This is called the "NPK" ratio.
It's always a good idea to keep your nutrient supply fresh. We recommend using all nutrients in a year or less. The chemical elements inside the package are in a concentrated form and they deteriorate over time.