Someone recently mentioned that they keep seeing or hearing the term "allograft" in reference to transplants but wern't sure what the term meant. Here is an easy to understand definition of this and similar terms.
An allograft is a transplanted organ or tissue from a genetically non-identical member of the same species. Most human tissue and organ transplants are allografts.
In contrast, a transplanted organ or tissue from a genetically identical donor, i.e. an identical twin, is called an isograft, while a transplant from another species is termed a xenograft. When a tissue is transplanted from one site to another on the same patient, such as a skin graft or a tissue flap, it is termed an autograft.
Allografts and xenografts will be recognized by the recipient's immune system as foreign and will therefore be attacked in a process termed rejection; this does not occur in autografts or true isografts (although in practice, transplants between identical twins are usually covered with immunosuppressants in case they are not 100% genetically identical).