Here are some helpful definitions of some terms you see around this site:
Transgender – “Identified with a gender other than the biological one.” Transgender is a very broad term for anyone that feels their gender identity doesn’t conform to the one assigned at birth. Under this umbrella term there are several sub-groups, some described below. There is still some ongoing debate about what does and doesn’t fall under this “umbrella” term.
Transsexual – “A person who has undergone surgery and/or hormone treatment in order to acquire the physical characteristics of the opposite sex.” Being transsexual isn’t about “sexual activity”, it’s not talking about that (there are many transsexuals who are celibate for example). Instead, it’s describing individuals for whom their gender incongruence is so strong, they seek medical treatment through hormone therapy, and sometimes (but not always) physical surgery.
MTF – Male to Female. This is often paired with the word “transsexual” to describe individuals who are undergoing therapy to go from male to female. (i.e. MTF Transsexual)
FTM – Female to Male. (See above)
HRT (Hormone Replacement Therapy) – The medical process of artificially modifying the body’s hormone levels. In the case of an MTF individual this typically means the lowering of the male hormone testosterone, and supplementation with the female hormone estrogen. The reverse is true for FTMs.
Transition – Transition is the word used to describe the process of moving from one gender to the other gender. This process usually takes several years, and can involve the help of supportive family and friends, medical doctors, psychologists, speech therapists, surgeons, and more.
Full Time – Full time is the time at which a trans person begins living “full time” (24/7) as their target gender.
Cisgendered – “Not transgender; identifying with the same social gender as most people with the same biological sex” or “Someone who associates and is comfortable with the gender they were assigned at birth.”
Other related definitions: