“Trans” encompasses almost anyone who doesn’t identify with the gender assignment given to them at birth. It is the superset term that includes transgender, genderqueer/non-binary, agender, and other individuals who are disagree with their “assigned gender at birth” but refuse to get a sex change. (Whereas “transsexuals” are people who work towards getting, or have underwent, a sex change.)
More than mere gender variance, being trans leads to a condition known as “ gender dysphoria”, where you were born one sex, but wish to live as a member of the other.
Unlike the majority of “trans” people, I believe you have to suffer gender dysphoria and undergo a sex change, a view often called transmedicalism.