The fact of being who or what a person or thing is (Oxford Dictionaries)
Sounds pretty simple when you say it that way. Yet, there is a vast amount of academic research and countless studies on the topic of identity...its definition, how it forms--is nurtured or stunted and its significance to individuals, and their interactions within society.
Here are just a few resources to guide our understanding of the LGBTQAI identity process
Cass Identity Model
D'Augelli's Identity Model
Stages of Transsexual and Transgender Identity Formation
A little something more entertaining about the gender identity distinction