This is a very heated topic for some, personally, I believe you should be who you areas long as you’re happy. There are plenty of ignorant people in the world looking for people to hate. The reason I am doing this series is because I know people in my life that fall into numerous categories. Also, it should be noted that gender identity is not the same as sexuality or sexual preference.
The discussion of gender identity is very complex and I will do my best to give a breakdown here but I will not get all of of the information in this post. There will be will be numerous sources listed at the bottom that will go into more detailed information. Also, there are extensive, complex differences for gender identity so I will note the major ones and there are several sites listed in sources that go into the entire list.
Gender identity is the personal sense of gender, that may be the assigned sex at birth or it can be a different gender that a person identifies as. Obviously everyone is aware of Cisgender male and female, which is typically classified as masculine, feminine and is the gender you were assigned at birth.
According to Wikipedia, a person’s gender identity is usually formed by the age of 3. Studies have shown that usually by 3 years old gender identity is formed and children can make firm statements about their gender, and tend to choose toys and activities which are appropriate for their gender. “Gender identity refinement extends into the fourth and sixth years of age and continues into young adulthood.”
Transgender is defined as a person who identifies as the opposite sex they were assigned at birth. There have been numerous studies of the brains of people who are transgender and note that their brains have “sexually dimorphic brain structures”, noting that the basal ganglia of transgender female looks more like the brain of someone assigned female at birth, the same for transgender males.
Nonbinary is defined as a person who does not strictly identify as male or female. In this article on healthline states “some people who are nonbinary experience their gender as both male and female, and others experience their gender as neither.”
Gender identity comes with pronouns as well so make sure you ask what their preferred pronoun is.
Sources: https://deconforming.com/gender-identities/, https://www.plannedparenthood.org/learn/gender-identity/sex-gender-identity, https://www.hrc.org/resources/sexual-orientation-and-gender-identity-terminology-and-definitions, http://thepbhscloset.weebly.com/a-list-of-genders–sexualities-and-their-definitions.html, https://www.itspronouncedmetrosexual.com/2013/01/a-comprehensive-list-of-lgbtq-term-definitions/, https://en.wikipedia.org/wiki/Gender_identity, https://www.cbsnews.com/news/transgender-gender-identity-terms-glossary/