What is a derived character?

A "derived character" is a trait that arose in the most recent common ancestor of a particular lineage and was passed along to its descendants.

Among a given group of organisms, the shared derived characters are generally the less common characters. The evolutionary interpretation is that these characters of organisms are more recently evolved. They are contrasted with primitive characters. Shared derived characters should have the same structure and function.

Derived characters may be present in members of one group of the line, but not in the common ancestor. For example, in comparing fish and mammals, fish have scales and mammals have hair. So having hair is a derived character for mammals, as only the mammals have ancestors with hair.