What is a baby's first poop known as?

Meconium is a newborn's first poop. This sticky, thick, dark green poop is made up of cells, protein, fats, and intestinal secretions, like bile. Babies typically pass meconium (mih-KOH-nee-em) in the first few hours and days after birth. But some babies pass meconium while still in the womb during late pregnancy.

Source: Kids Health