Presence of precipitates
Cloudiness indicates light scattering by small particles, with size on the order of the wavelength of light and larger. If those small particles are denser than the liquid, they may eventually sink and become the settled precipitate.

However, some small particles are so small and so nearly equivalent in density to the liquid that they do not sink, but remain suspended. Brownian motion helps. Some clays can remain suspended indefinitely; in water treatment plants, FeCl3 is used as a flocculant to bring such turbidity down. 

Sometimes intermolecular interactions keep particles suspended. For instance, many surfactants form micelles comparable in size to the wavelength of light and may, in pure form, be considerably more, or less, dense than the liquid, and yet remain suspended indefinitely because they are at least partially hydrophillic. 

Centrifugation may help bring down suspended particles (or float them if they are lighter than water).