Clone

A clone is any cell or individual which is identical to another.
In biology, cloning is the process of producing one or more genetically identical individuals. With whole individuals, it usually means the deliberate production of an identical copy. This was first achieved in mammals with the famous Dolly the sheep. Human identical twins are "natural clones". So are the offspring of asexual reproduction, and any parthenogenetic reproduction which does not involve meiosis.
Cloning is natural to some animals, but rare in mammals. An exception is the nine-banded armadillo, which normally gives birth to identical quadruplets.
In genetics and cell biology, cloning refers especially to the DNA sequence, and by implication all the other macromolecules.
Clones in cell lines occur, but there are some obvious provisos. Changes to the DNA in any shape or form means the daughter cells are not identical with the mother cells. Typically during development genes are switched on and off, and the daughter cells gradually become differentiated into mature tissue cells. These are not identical with the original stem cells, so they are clones only in the sense of being "derived" from the same mother cell.
The laboratory copying of a molecule to produce exact copies is also called cloning.
Not quite so identical.
Although clones start off identical, they may not stay that way. Identical twins always have slightly different phenotypes.
Although monozygotic twins are genetically "almost" identical, a 2012 study of 92 pairs of monozygotic twins found that monozygotic twins acquire several hundred genetic differences early in foetal development. This is caused by mutations (or copy errors) taking place in the DNA of each twin after the splitting of the embryo. It is estimated that, on average, a set of monozygotic twins will have about 360 genetic differences that occurred early in foetal development. However, these changes may have little practical effect. In practice, identical twins look and act in a very similar way.
Another cause of difference between monozygotic twins is epigenetic modification. These are caused by differing environmental influences throughout their lives, which affects which genes are switched on or off. A study of 80 pairs of monozygotic twins ranging in age from three to 74 showed that the youngest twins have relatively few epigenetic differences. The number of epigenetic differences increases with age. Fifty-year-old twins had over three times the epigenetic difference of three-year-old twins. Twins who had spent their lives apart (such as those adopted by two different sets of parents at birth) had the greatest difference. However, certain characteristics become more alike as twins age, such as IQ and personality. This phenomenon illustrates the influence of genetics in many aspects of human characteristics and behaviour.