Autogynephilia

Autogynephilia is when a person (usually a man) finds themselves attracted to the idea of being a woman, or imagines themselves as a woman. They may dress up, act like a woman, and even become sexually aroused by their own femininity. This is different from being transgender (which is when a person's gender identity doesn't match their physical bodies), because with autogynephilia the person is still identifying as the same gender they were born with, just with a strong attraction to being a woman.