The umbilical cord is the tube full of blood vessels that connects you to your baby while you're pregnant. The cord comes out of the baby's belly button, which is called the umbilicus. The umbilical cord carries blood with nutrients and oxygen from your placenta to your baby. When you give birth, usually the baby is delivered first and then the umbilical cord comes out after the baby.
Prolapse means something has fallen out of where it belongs. A prolapsed umbilical cord is an umbilical cord that has fallen out in front of your baby during delivery. When this happens, the umbilical cord can get pinched shut between your baby and your pelvic bones. This cuts off the baby's blood supply, which can be rapidly fatal.
If the cord is sticking out of your vagina, you will need to have a C-section right away. Until surgery begins, a nurse or doctor holds the baby's body off the cord so that the blood supply isn't cut off.
If the cord isn't sticking out of your vagina, doctors will have you lie in a different position to take pressure off the cord. You may need a C-section if this doesn't work.