"Afterbirth pains" refers to the cramping sensations a woman experiences after delivering a baby. These pains happen because the uterus is contracting to return to its pre-pregnancy size. Full definition
It takes a few weeks for the process to finish, but you may feel those contractions soon after giving birth, which are also known as afterbirth pains. (romper.com)
You'll probably have more intense afterbirth pains. (babycenter.com)
You may feel light contractions called afterbirth pains for a few hours or days, particularly when you're nursing your baby. (babycenter.com)