Diethylstilbestrol (DES) is a big word to pronounce, and it is a kind of medicine that was given to women who were expecting babies in the past. It was given to the mommy to help them not lose their baby during pregnancy.
Sometimes, when a mommy is pregnant, they are at risk of losing their baby. To help keep the baby, doctors give the mommy some medicine. DES was a kind of medicine that helped to stop the mommy from having an early delivery.
But, later on, it was discovered that DES could also create problems for babies, especially girls. Girls born from mommies who took DES had a bigger chance of getting cancer in their uterus when they turned into adults.
So, it isn't used anymore, and if your mommy or grandma took this medicine while they were pregnant, you might need to talk about this with your doctor to check that everything is okay.