Soil is a heterogeneous mixture. Soil is made up of a variety of substances, such as pebbles, plant matter and sand, but these components remain separate in the mixture.
A heterogeneous mixture is non-uniform; that is, it's not the same throughout the entire mixture and the different parts can be seen. Another example of a heterogeneous mixture is cereal in milk. Homogeneous mixtures, on the other hand, are uniform in composition, with each part not visibly separate and therefore not distinguishable from each other. An example of this is salt dissolved in water. The salt spreads evenly in the water when it dissolves so that all parts of the solution are the same.