"Transgirl" and "Transwoman" are terms used in the context of adult content to describe transgender women.
Transgender is an umbrella term for people whose gender identity, expression or behavior is different from those typically associated with their assigned sex at birth. Transwomen (or transfeminine individuals) are individuals who were assigned male at birth but identify as female. Similarly, transgirls are transfeminine individuals who may be younger or less experienced than other transwomen. Both terms refer to the same concept and can be used interchangeably in this context.