"Trans" is often used as an abbreviation for "transgender". Transgender people have a gender identity (how they feel inside) different from the gender they were assigned at birth. For example, a trans man feels he is a man even though he was biologically identified as a woman at birth. It is about how people perceive themselves and how they identify, which may not correspond to their biological sex.
Trans: The Sexiom Handbook
Definition and designation of the term Trans from the Sexiom Handbook. Quick and briefly.