Identical twins are siblings who are born at the same time, from the same mother, and who are genetically the same. It can be hard to tell one identical twin from the other, because they look alike.
There are two types of twins: fraternal twins, who look different, and identical twins, who look very similar to each other. All twins are carried at the same time by their mother, but identical twins also have the exact same DNA, or genes, because they develop from the same fertilized egg. Identical twins are also called monozygotic or monozygous twins. The adjective identical comes from the Medieval Latin identicus, which means "the same."