Matter is anything that has mass and takes up space. It can be classified based on physical and chemical properties. Physical properties describe matter without changing its composition, and include intensive properties like density and color, as well as extensive properties like mass and volume. Chemical properties allow matter to undergo changes that alter its composition through chemical reactions. Matter can also exist as pure substances or mixtures. Homogeneous mixtures like solutions are uniform mixtures, while heterogeneous mixtures like suspensions may separate over time due to differences in phase or particle size.