I imagine you are referring to a dichotomous key is a type of method used by many researchers to identify an organism. Through this kind of key, we can, for example, know the species of plant we are looking at. Just follow the key steps! It is called dichotomous because it allows two inputs. An example of parallel choice in a dichotomous key is the entries "a. Flower color is red; aa. Flower color is blue" that indicate two different response types.
