Colloids dispersion classification
Words like "homogeneous" and "heterogeneous" do not have a well-defined meaning.  Different authors use them differently.  The fact is, all matter is made of atoms, and atoms are not homogeneous.  Thus, from a certain point of view, nothing is homogeneous.  Matter is lumpy!

But suppose we don't care about things on the scale of atoms, i.e. angstroms.  Then the question is "what scale do you care about?"  Nanometers?  Hundreds of nanometers?  Chemists are making materials that have lumpiness on more more less all of these scales.  

Back before folks invented centrifuges, filtration, and microscopes, bacterial cultures, with cells as small as 1 &mu;m in diameter, probably seemed homogeneous.  But van Leeuwenhoek peered through a microscope and dispelled that notion.