Contextual explanation: Composed of dissimilar elements. 
Heterogeneous is best understood as a quality—specifically, a distinguishing characteristic describing something made-up of parts that are different from one another. This term applies to objects, groups, systems, or environments where variety and diversity are defining features.

Themes: Diversity and variation. 
Heterogeneous is closely tied to the theme of diversity, as it highlights the presence of multiple, distinct components within a whole. This theme is relevant in contexts ranging from science (heterogeneous mixtures), to society (heterogeneous populations), to technology (heterogeneous networks), emphasising the importance of variation and non-uniformity.

Nuance: Mixed composition. 
What distinguishes heterogeneous within its category is its focus on the coexistence of unlike or varied elements, rather than uniformity or sameness. The nuance lies in the recognition that the parts retain their distinct identities within the whole, contributing to complexity and richness in structure or function.