Gender binarism is a social construct based on the idea that society only has two genders—feminine and masculine—which are assigned at birth. These correspond to the sex assigned at birth.
In other words, when a person is born with a female reproductive system, the sex assigned to them is woman, and their gender is expected to be female. When a person is born with a male reproductive system, the sex assigned to them is man, and their gender is expected to be female. This practice and hierarchical organization system implies that everyone must be categorized, or categorize themselves.
Today, many societies still consider that the man-woman division is the model for social organization. A person who does not identify with the sex they were assigned at birth is considered to be experiencing a pathology.
Despite the fact that this is a generalized social construct, there are examples in the 18th century of societies that did not follow this binary system, such as the Neapolitan. Currently, there is an open debate regarding the limitations and strict nature of this social system, and the consequences for people who do not identify with it.