Final answer:
The stool that a newborn passes within 24 hours after delivery is called meconium.
Step-by-step explanation:
The stool that a newborn passes within 24 hours after delivery is called meconium. Meconium is a tarry, greenish-black substance that accumulates in the fetal intestines during the second half of gestation. It is the newborn's first stool and is typically replaced by seedy yellow stools or slightly formed tan stools as the baby digests breast milk or formula.