The group of animals or plants related by descent and similar in most characteristics is called a species.

Here's a breakdown:

* Related by descent: This means they share a common ancestor.

* Similar in most characteristics: This includes physical traits, behaviors, genetic makeup, and the ability to reproduce with each other.

So, for example, all dogs belong to the species *Canis lupus familiaris*. They share a common ancestor with wolves and are similar in many ways, but they are distinct from other species like cats or horses.