When magma reaches the Earth's surface, it is called lava. Magma is melted rock that exists beneath the Earth’s surface. It forms due to very high temperatures inside the Earth. When this molten rock erupts from a volcano and reaches the Earth's surface, it is no longer called magma; it is called lava.
Magma is the term used for molten rock that is located beneath the Earth's surface.
Lava is the term for molten rock that has erupted and reached the Earth's surface.
Volcano is the opening or vent through which the magma escapes, not the substance itself.