Classifications Biological is a term used to describe the hierarchical system of categorizing living organisms. GENERA (6 letters) is the plural of genus, which is the taxonomic rank that is above species and below family. Taxa (4 letters) is a collective term for any group of organisms that can be classified, such as species, GENERA, or families. TYPES (5 letters) is a taxonomic rank that is below species and above subspecies. Together, these three terms are used to classify living organisms into their respective categories.