What is water-soluble garden fertilizer?

Generally, water soluble fertilizer would be an inorganic fertilizer like Miracle Gro. You will notice that organic fertilizers have NPK under 10. For example, Gardens Alive company has a fertilizer called Tomatoes Alive which has NPK of 6-2-2. Miracle Gro has an NPK something like 37-17-10. This is because it is water soluble and dissolves quickly out of the soil, whereas the organic fertilizers persist in the soil and are gradually broken down by soil organisms to make the nutrients available to the plant.