Female (left) and male (right) duck
Genitals are the sex organs of an organism's body, commonly detoniting one of *multiple 'sexes' that decide the organism role is reproduction. For humans genitals are usually used to categorize gender. However how the person presents does not always align with this.
second example, for clarity
For other animals their genitals may decide a larger part of their appearance, an example of this is sexual dimorphism such as that of ducks.
A organism genitals are usually determined by chromosomes-- this is most evident in mammals--males typically have XX chromosomes and males typically have XY chromosomes.