A clone is simply a genetic duplicate of an organism, or more simply one living thing made from another, leading to two organisms with the same set of genes. In that sense identical twins are clones because they have the same genetic make-up. Using cuttings clones many plants. When earthworms are cut in half, they regenerate the missing parts of their body, leading to two worms with the same set of genes. But the ability to intentionally create a clone in the animal kingdom by working on a cellular level is a very difficult and very recent development.
Scientists take a cell from a donor animal and culture it for several weeks.
Then they harvest an unfertilized egg from a second animal and remove the nucleus, the part that contains the genetic material, after starving them for a few days. By starving the donor cells for a few days before extracting their nuclei, scientists force the cell into the dormant phase, which is when the cell becomes nutrient deprived and its genes begin to deactivate. The nuclear DNA is now susceptible to being reprogrammed once placed in an egg. Electricity may be used to combine the two cells. The egg then begins dividing as a naturally fertilized egg would, becoming an embryo.