A definition is expected to identify the intended definiendum. If the expression is so broad that it includes many other species, it does not adequately exclude what is outside the target.
For example, “Human is an animal” is true as a generic classification, but animal also applies to horses and numerous other species.
Naming a genus can be useful introductory information. It is not, by itself, the complete definition. An essential differentia or a distinguishing property supplies the missing discrimination.