Human cloning is the creation of a genetically identical copy of a human. It does not refer to monozygotic multiple births or the reproduction of humans/animals cells or tissue. The ethics of cloning is an extremely controversial issue. The term is generally used to refer to artificial human cloning; human clones in the form of identical twins are commonplace, with their cloning occurring during the natural process of reproduction.
There are two commonly discussed types of human cloning: therapeutic cloning and reproductive cloning. Therapeutic cloning involves cloning cells from an adult for use in medicine and transplants, and is an active area of research. Reproductive cloning would involve making cloned humans, for couples wanting to have a child, but cannot naturally.
A third type of cloning called replacement cloning is a theoretical possibility, and would be a combination of therapeutic and reproductive cloning. Replacement cloning would entail the replacement of an extensively damaged, failed, or failing body through cloning followed by whole or partial brain transplant or harvesting the internal organs of the clone.