The gender binary is composed of the genders male and female, which are known as the binary genders. A nonbinary gender, by contrast, is any gender that is not fully and/or not always male or female, including genders that are neither male not female at all.
Most people are assigned a binary gender at birth based on their genitalia. If their identity matches that gender, they are cisgender. If their identity does not match that gender, they are transgender. Transgender people can have a binary or nonbinary gender.