When someone identifies as binary, it means they identify as either male or female. The word "binary" usually relates to two choices, and in this case, it refers to the male and female gender.
While traditional society has proposed that there are only two genders that align with the two biological sexes, more evidence is pointing to the existence of genders outside the binary, and more people are identifying as non-binary (i.e., identifying with neither male nor female genders).
People who identify as binary usually follow traditional gender norms, expressions, and roles. For example, this looks like females dressing feminine and taking on the majority of household work like cleaning and raising children, while males may take on more physically demanding jobs outside the home.
While these binary roles were once common in our society and around the world, more people have challenged these traditional roles in recent years. In addition, scientists are learning more about sexuality and gender than was ever known before.