Nanodispersion is a special kind of colloid dispersion containing dispersed nanoparticles. Terms “colloid” and “colloidal” are not always exactly de ned but commonly refer to small entities. A colloid entity has at least one colloidal dimension. Colloid particles, such as small spheres, have three colloidal dimensions. Colloidal thin lms have two colloidal dimensions while thin bers are one-dimensional colloids. Colloid dispersion is a system in which colloid particles are dispersed in a medium. e question is, what is colloidal dimension? A simple, but not always correct, answer is “below 1 μm and above the molecular size of, e.g., 1 nm.” Another answer is more correct, but less clear: “Particles are colloidal if they exhibit colloidal behavior.” is “de nition” obviously requires clari cation. Under “colloidal behavior” one understands that colloid particles exhibit not only the behavior of a (macro) phase but, at the same time, also the behavior of molecules. Macroscopic properties are, e.g., de ned structure, surface plane, interfacial tension, and size large enough for molecular medium to behave as homogeneous phase of de ned viscosity. Molecular properties are related to Brownian motion, mutual collisions of particles. It should be noted that colloid particles are o en aggregates of nanoparticles.