Adverse reaction:  An unintended side effect of a drug.

Advocacy organization:  A group that helps someone get what they need or want, promotes a certain point of view, or pleads the case of another.

Allocation: The process of determining how organs are distributed. Allocation includes the system of policies and guidelines which ensure that organs are distributed in an equitable, ethical and medically sound manner.

Allograft: An allograft is a transplant of an organ or tissue that comes from another person of the same species. For example, in intestinal transplant the allograft is the intestine.

Aneurysm: An aneurysm is a ballooning or weakened area in the wall of a blood vessel. As it increases in size, the risk of rupture increases, which can lead to internal bleeding and death. This is a common cause of brain death in deceased donors.

Anti-Rejection Medicine (immunosuppressive drugs): Medicines that reduce or prevent the body's ability to reject a transplanted organ or tissue. Examples include: Tacrolimus (Prograf), Sirolimus (Rapamycin), Mycophenolate (Myfortic).

Antibody: A protein substance made by the body's immune system to attack a foreign substance, for example, a blood transfusion, virus or pregnancy. Because antibodies attack transplanted organs, transplant patients must take powerful drugs to reduce the body's attack on the transplanted organ. See anti-rejection medicine.

Antigen: A foreign substance, such as a transplanted organ or tissue, that triggers the body to reject it (destroy it.)

Ascites: A buildup of fluid in the abdomen usually associated with liver disease.