**Core Concept**
The transfer of a graft from a different species is a complex immunological phenomenon that involves the interaction between the donor and recipient's immune systems. This process is crucial in understanding xenotransplantation, where organs or tissues are transplanted across species boundaries.

**Why the Correct Answer is Right**
The term "xenograft" refers to a graft that is transferred from a donor of a different species to a recipient of a different species. This occurs when an organ or tissue is transplanted from one species to another, such as from a pig to a human. Xenografts trigger a strong immune response due to the presence of xenoreactive antibodies, which recognize the graft as foreign. The major histocompatibility complex (MHC) molecules on the surface of the donor cells also play a crucial role in the immune response.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the transfer of a graft across species boundaries. Allografts involve the transfer of a graft between two individuals of the same species.
**Option B:** This option is incorrect because it is a type of graft that involves the transfer of a graft between two individuals of the same species, not across different species.
**Option C:** This option is incorrect because it refers to a type of graft that is transferred from a donor of the same species as the recipient, not from a different species.

**Clinical Pearl / High-Yield Fact**
Xenotransplantation is a rapidly advancing field, with researchers exploring the use of genetically modified pigs as donors for human transplantation. However, the risk of xenozoonotic disease transmission, such as porcine endogenous retroviruses (PERVs), remains a significant concern.

**Correct Answer:** C.