Why do we say identical twins is a type of cloning?

It's because one type of twins, the identical twins (=monozygotic), are the result of the same egg+sperm that just divided one more time to produce two humans. That's pretty much the meaning of the word monozygote. read more

Non-identical twins are produced from different egg and/or sperm cells, so they are not clones. Cloning means, to produce a clone from an existing individual. We don’t say having identical twins is cloning, because they’re not copying an original. read more

Human cloning is the creation of a genetically identical copy of a human. The term is generally used to refer to artificial human cloning, which is the reproduction of human cells and tissues. It does not refer to the natural conception and delivery of identical twins. read more