Igneous rocks that formed beneath the surface are called intrusive or plutonic rocks.

Here's why:

* Intrusive: They formed from magma that cooled and solidified *inside* the Earth's crust.

* Plutonic: This term refers to the god Pluto, who ruled the underworld. It's used to describe rocks that formed in the "underworld" of the Earth's crust.

Some common examples of intrusive igneous rocks include granite, diorite, and gabbro.