What is Colloid?

A colloid is a dispersion of particles, droplets or bubbles, roughly $1\,\mathrm{nm}$ to $1\,\text{µ}\mathrm{m}$ across (the dispersed phase), in a continuous dispersion medium. A sol is a dispersion of solid particles in a liquid, an emulsion of liquid droplets in another liquid, a foam of gas bubbles in a liquid or a solid, a gel a network of particles or polymers that spans the whole liquid and makes it solid-like, an aerosol of droplets or particles in a gas.