Final answer:
Vernix caseosa is the thick, greasy substrate that covers the newborn immediately after birth. It protects the newborn's skin from amniotic fluid.
Step-by-step explanation:
The thick, greasy substrate immediately following birth is called vernix caseosa. Vernix caseosa is a waxy coating that protects the newborn's skin from chapping or irritation caused by amniotic fluid. It is composed of dead skin cells and sebaceous secretions from the fetus.