Molten material within the Earth is called magma. In simple terms magma can be thought of as molten rock. When magma cools, it solidifies to form rock which is called "igneous rock".

What do you call the molten rock underground?

Scientists use the term magma for molten rock that is underground and lava for molten rock that breaks through the Earth's surface.

What is lava called before it reaches the surface?

Before lava reaches the surface, the molten material is called magma.