Mixture is a combination of two or more different substances that have not combined chemically. Compounds can be contrasted from mixtures as combination of two or more elements that have combined chemically.
Homogeneity of a mixtures refers to the degree of uniformity of composition. Mixtures vary in the degree of heterogeneity they possess, from highly homogeneous to highly heterogeneous mixtures. All mixtures are heterogeneous at molecular level. Similarly, a perfect heterogeneous mixture would require its component substances to be completely separate from each other. A material like that will not meet the basic definition of being combination of more than one material. However mixtures in form of solution and gaseous forms, which are heterogeneous at molecular level only are classified as homogeneous, while all other mixtures are classified as heterogeneous mixtures. Some solutions when solidified also form homogeneous mixtures.
One important difference between homogeneous and heterogeneous mixtures is that components of homogeneous mixtures cannot be separated by centrifugation, while those of heterogeneous mixtures can be separated.
Moving from lowest homogeneity to higher homogeneity the next level mixtures are colloidal solution. This is followed by followed by dispersions.