In biological classification, a group of closely related families is known as what?

In biological classification, a group of closely related families is referred to as an order. The hierarchical structure of classification, known as taxonomy, is organized into several ranks, including domain, kingdom, phylum, class, order, family, genus, and species.

In this structure, families represent a more specific grouping of organisms that share certain characteristics and evolutionary traits. Several of these families grouped together form an order, which includes multiple families that are closely linked through shared features and evolutionary history. This level of classification helps biologists communicate about relationships and similarities among different groups of organisms, providing a clear framework for biological diversity.

The other ranks listed do not represent a grouping of families; for instance, family is a more specific level than order, while class encompasses multiple orders. Genus is a rank that consists of one or more species, which is even more specific than family. Thus, choosing order accurately reflects the relationship being asked about in the question.