Meconium is the first stool passed by a newborn baby. It is a thick, sticky, and dark green substance that is made up of a variety of substances, including:

* Mucus: A sticky substance that helps protect the baby's airways.

* Bile: A digestive fluid that helps break down fats.

* Amniotic fluid: The fluid that surrounds the baby in the womb.

* Skin cells: Cells from the baby's skin.

* Lanugo: Fine hair that covers the baby's body.

The composition of meconium can vary depending on the baby's health and the length of the pregnancy.