An igneous intrusion is a body of magma that has forced its way into pre-existing rocks and solidified beneath the Earth’s surface. Types of intrusions include dikes, sills, laccoliths, and plutons. These features are important in understanding the structure of the Earth’s crust, the formation of mineral deposits, and the processes of magmatic emplacement.
Reference: Pitcher, W. S. (1997). The Nature and Origin of Granite. Springer.