Gender identity is a person's private sense of their own gender. This is separate from their assigned sex and appearance. Because gender identity is an internal experience, it cannot be assigned, diagnosed, measured or disproved by anyone else—a person's gender identity is their own.
Every person thinks of their own gender slightly differently, but there are a common set of labels that most people find helpful in communicating their identity to others. These gender identity labels include, but are not limited to, man, woman, cisgender, transgender, third gender, and non-binary. Pressuring someone into a label they do not relate to can result in dysphoria.