It is usally a genetic male, who has taken female doses of estrogens (premarin, estrofem) to become biologically female in all aspects except that she still has a penis and testicles instead of a vagina, uterus, and ovaries. They do not get breasts from breast implants, but from female doses of estrogen. They sometimes get implants to augment the breasts that they have gotten from taking estrogen. Their gender identity and expression is female. Most gay guys dont like them, but bi-curious "straight" males tend to like them.
Allanah Starr, Vicki Richter, and Joanna Jet are all shemales.