Colloid, Dispersion phase and dispersion medium
Origin of study of colloid starts with Thomas Graham who observed diffusion of that a solution of sugar, urea or sodium chloride through a membrane but not glue, gelatine or gum. He called the former substances as crystalloids and the latter as colloids ( In Greek, kola as gum, eidos-like).
Later it was realised that any substance can be converted into a colloid by reducing its particle size to 1-200nm.
Hence, colloid is a homogeneous mixture of two substances in which one substance (smaller proportion) is dispersed in another substance( large proportion).
In a colloid, the substance present in larger amount is called dispersing medium and the substance present in less amount is called dispersed phase.