What is the term for melted rock that erupts on Earth's surface?

The correct term for melted rock that erupts on Earth's surface is lava. When a volcano erupts, the molten rock that flows from it is referred to as lava. This is different from magma, which is the term used for molten rock that exists beneath the Earth's surface. When magma reaches the surface and erupts, it is transformed into lava.

Igneous rock is a type of rock that forms from the cooling and solidification of lava or magma, while metamorphic rock is formed from the transformation of existing rock types through heat, pressure, or chemically active fluids. Therefore, lava specifically denotes that the molten rock is encountered at the surface following a volcanic eruption.