How do solutions differ from heterogeneous mixtures? Other classes of matter?
Heterogeneous solutions are usually called suspensions and they occur when there are two distinct parts about the solution. Homogeneous solutions have only one distinct phase.
Consider salt water, a homogeneous solution where sodium chloride has completely dissolved in water. Think of other examples when the solution only has one distinct part, or when the constituent solute is completely dissolved by the constituent solvent within the solution, these will be homogeneous solutions.
Now think of oil and water, which will settle into two distinct parts. These can sometimes also be different phases of matter, and then it would be more correct to call it a heterogeneous mixture. Oil and water is a heterogeneous solution, and will form a colloid to become a suspension.