First, the difference between sex and gender is important to note. Gender is an internal sense of being male or female and is based on societal or cultural definitions of masculine or feminine. Sex refers to differences in chromosomes, hormones and external and internal sex organs.
A person whose sense of identity does not correspond with their birth sex – for instance, a man who, despite having male genitalia, feels he is a woman – is considered transgender. Often, transgender people say they feel they were born in the wrong body.
What is transsexual?
A transsexual is a person who feels he or she belongs to the oppopposite sex, and has a desire to assume the physical characteristics and gender role of the opposite sex. The transsexual person may use hormones or other medications to suppress or enhance characteristics of the opposite sex – such as facial hair, or more developed breasts.
Some transsexuals choose to have gender reassignment surgery – or surgery where a person's physical sexual characteristics are changed by surgery or hormone treatment.
Gender reassignment surgery, presumably the cost Trump was referring to in the tweets, averages around $140,450 to transition from male to female, and $124,400 to transition from female to male, according to the Philadelphia Center for Transgender Surgery. Those prices include hospital stays, anesthesia and other costs associated with surgery.
Sources: American Psychological Association; The Associated Press; The Philadelphia Center for Transgender Surgery