A dispersion is a material comprising more than one phase where at least one of the phases consists of finely divided phase domains, often in the colloidal size range, dispersed throughout a continuous phase.

A continuous phase is a phase not interrupted in space.

A dispersed phase is a phase constituted of particles of any size and of any nature dispersed in a continuous phase of a different composition.

The dispersion medium is the matrix for the dispersed phase. The dispersion medium is the continuous phase of the dispersion.

Source from IUPAC: Terminology of polymers and polymerization processes in dispersed systems (IUPAC Recommendations 2011)*.

Depending on the size of the particles in the dispersed phase we have:

• Solution, for size less than a nanometer.
• Colloid, for size between a nanometer and a micrometer.
• Coarse dispersion, for a size larger than a micrometer.

"Dispersion", without adjective, is often used to refer to the colloidal regime.

Dispersion types

For phases with particles of colloidal size or larger. For smaller sizes, see solution.

See https://en.wikipedia.org/wiki/Dispersion_(chemistry) for examples.