Final answer:
Generalization/specialization is the concept based on classifying things in terms of similarities and differences, utilized in biological classification systems like the Linnaean system.
Step-by-step explanation:
The concept that is based on the idea that people classify things in terms of similarities and differences is generalization/specialization. In the context of biology and the classification of living organisms, this refers to the grouping of individuals or species based on shared characteristics while recognizing their variance. The Linnaean system, for instance, is a historically significant example of this kind of classification, where organisms are sorted into a hierarchy of taxa based on physical traits, despite the acknowledgment of its flaws due to non-natural grouping. The discussion of aggregation and multiplicity also touches upon the nature of classification, as these concepts contribute to understanding how entities can be grouped.