Sketch by B. Myers
Magma is molten or partially molten rock beneath the Earth's surface. When magma erupts onto the surface, it is called lava. Magma typically consists of (1) a liquid portion (often referred to as the melt); (2) a solid portion made of minerals that crystallized directly from the melt; (3) solid rocks incorporated into the magma from along the conduit or reservoir, called xenoliths or inclusions; and (4) dissolved gases.
This sketch shows a classic cartoon view of a magma reservoir beneath a volcano and a conduit leading up to a lava dome at the surface. The arrow indicates direction of magma movement from a deeper source.