First of all, colloid is not a special substance, nor is it the nature of matter, but a special state of matter. The colloidal system is characterized by the dispersed phase particles having a certain size (the diameter of the dispersed phase particles is 1~100nm), and there is an obvious physical interface between the colloidal particles themselves and the dispersion medium, so the colloidal system is a two-phase or multi-phase inhomogeneous dispersion system.