A colloid is any substance that is made of particles that are of an extremely small size- larger than atoms but generally have the size of 10^-7 cm ranging to 10^-3 cm. Repulsive forces between charged particles having the same charge prevent them from colliding when they come across each other. As a result of which, presence of equal and similar charges on colloidal particles provide stability to them due to repulsion. This erratic random movement of the particles is also termed as Brownian motion.