Twins are two offspring produced by the same pregnancy. Twins can either be monozygotic ("identical"), meaning that they can develop from just one zygote that will then split and form two embryos, or dizygotic ("fraternal"), meaning that they can develop from two different eggs, each are fertilized by separate sperm cells.
In contrast, a fetus which develops alone in the womb is called a singleton, and the general term for one offspring of a multiple birth is multiple.

  
Marian and Vivian Brown, identical twins, 
photographed by Christopher Michel

hello!

this blog is about TWINS!  

Hi, my name is Leo and my twins' name is Ari.  Me and my twin brother have created this blog to share the adventures we've had. We're ten years old, we love soccer, dogs, reading, music and climbing. We live in Eugene OR. in a small house with our mom, dad and six chickens.

Us on the dock in Florence.