A genus (pronounced “JEE-nus”) is a group of living things that share important characteristics and are closely related to each other. Scientists use the genus system to organize plants, animals, and other organisms into categories that make sense.

Think of it like organizing books in a library. All the mystery books go together, but within mysteries, you might group detective stories separately from spy thrillers. Similarly, all cats belong to the animal kingdom, but lions, tigers, and jaguars share so many features that scientists place them in the same genus, called Panthera, while house cats are in a different genus called Felis.

Every genus contains one or more species, which are even more specific groups. When scientists write an organism's full scientific name, they always list the genus first, followed by the species. Your pet dog belongs to the genus Canis and the species familiaris, written as Canis familiaris. Wolves, which are close relatives, are Canis lupus. Because dogs and wolves share the same genus, you know they're closely related and probably evolved from a common ancestor.

The plural of genus is genera (pronounced “JEN-uh-ruh”). When a biologist discovers a new type of beetle, one of the first questions is: which genus does it belong to?