Atwinis one of twooffspringproduced in the samepregnancy.[1]Twins can either bemonozygotic("identical"), meaning that they develop from onezygotethat splits and forms twoembryos, ordizygotic("fraternal"), meaning that they develop from two eggs, each fertilized by separate sperm cells.[2]
In contrast, afetuswhich develops alone in the womb is called asingleton, and the general term for one offspring of amultiple birthismultiple.[3]