Dispersion is defined as the action or process of distributing things or people over a wide area.
In the context of refraction, it means taking white light (white is a combination of all the colors) and separating them so that the colors are distributed spatially over a larger area.
In the diagram below a thin beam of light is directed into a glass prism. The colors are refracted in slightly different directions. Note how they are distributed as they exit the prism.