Extrusive igneous rocks form by the solidification of magma on the Earth's surface. A pluton is any body of intrusive igneous rock.
Plutons are masses of solidified magma that are exposed after erosion removes the overlying rocks.
A batholith is a pluton that is more than 40 square miles in size. The Sierra Nevada batholith in California is an example. A stock is a pluton that is less than 40 square miles in size. A dike is a tabular body of igneous rock that cuts across layered rocks. A sill is a tabular body of igneous rock that intrudes parallel to layered rocks.