The noun dispersion means the process of distributing something over an area. A combination of your yearly planting of new bulbs and their natural tendency to spread has led to the dispersion of daffodils over your entire back yard.
Dispersion refers to the act of spreading something, like your dispersion of sprinkles evenly over three dozen cupcakes. It can also be used to talk about the scattering of something across a very large range, such as the dispersion of people with Scottish heritage across the United States. The Latin root word is dispersione, which means a scattering.