 It's external and internal genitalia. It's hormones and chromosomes. That's something that you can only change with a whole lot of effort. Gender identity is how you feel inside. It's what you feel like in your heart and in your head, just like the language that we used when they were younger. But it's something personal. It's something that's unique to you. It's something that you get to decide. Gender expression is what you share with the world.