What is the term for a group of organisms in biological classification?

The term for a group of organisms in biological classification is "taxa." In biology, the classification system organizes living organisms into hierarchical categories based on shared characteristics and evolutionary relationships. Each category, or taxon (plural: taxa), can refer to various ranks in the hierarchy such as species, genus, family, order, class, phylum, or kingdom.

Taxa provide a systematic way to understand and communicate about the diversity of life on Earth, allowing scientists to identify and study the relationships among different organisms. This classification is essential for categorizing the vast diversity of species and understanding their evolutionary histories.

The other terms mentioned do not describe a group of organisms in classification. Homologous characteristics refer to traits that are similar due to shared ancestry, convergent evolution describes a process where unrelated species evolve similar traits, and plesiomorphy refers to an ancestral trait shared by a group that would not be useful in distinguishing it from other groups.