What term describes a mixture that is not uniform throughout?

A mixture that is not uniform throughout is described as heterogeneous. In such a mixture, individual components can be seen and identified, indicating that they do not blend uniformly at the microscopic level. This can often result in a composition that varies from one part of the mixture to another, making it possible to distinguish between different phases or substances within the mixture.

In contrast, a solution refers to a homogeneous mixture where the components are fully dissolved and cannot be distinguished from one another. Homogeneous mixtures are characterized by uniformity in composition and properties throughout, while a substance typically refers to a form of matter that has a uniform and definite composition, which is distinct from the concept of a mixture.