This document defines colloids and discusses their properties. Colloids have dispersed particles between 1-2000 Angstroms, making them intermediate between true solutions and suspensions. The document describes different types of colloids based on their dispersed and dispersion phases, such as solid-solid, solid-liquid, and liquid-gas colloids. Preparation methods include mechanical dispersion, electro-dispersion, ultrasonic dispersion, and peptization. Properties of colloids discussed include their kinetic, optical, and electrical behaviors.