Amazing, miraculous human beings. They come from the splitting of a fertilised egg, and look exactly the same. They have the same DNA, so one could commit a crime and frame the other one. (Although this never happens because identical twins are loving, friendly, law-abiding people).
Do not confuse with Non-Twins.
"Wow look at those two, they look exactly the same! They're helping that old lady cross the road, how kind!"
"Yeah they're identical twins, aren't they amazing?"
The term used to describe two babies born at the same time but are not identical. They do not come from the same egg and therefore have no right to call themselves twins, or even "non-identical twins". They are simply useless freaks of nature.