A dispersion is a system in which distributed particles of one material are dispersed in a continuous phase of another material.  The two phases may be in the same or different states of matter.
Dispersions are classified in a number of different ways, including how large the particles are in relation to the particles of the continuous phase, whether or not precipitation occurs, and the presence of Brownian motion.  In general, dispersions of particles sufficiently large for sedimentation are called suspensions, while those of smaller particles are called colloids and solutions.