A large mass of intrusive igneous rock that is beneath the Earth's surface is called a pluton.

Here's a breakdown:

* Intrusive igneous rock: This type of rock forms when magma (molten rock) cools and solidifies beneath the Earth's surface.

* Pluton: This is the general term for any large body of intrusive igneous rock.

* Batholith: A very large pluton, often covering hundreds of square kilometers.

* Stock: A smaller version of a batholith.

* Dike: A sheet-like intrusion that cuts across existing rock layers.

* Sill: A sheet-like intrusion that runs parallel to existing rock layers.

Let me know if you'd like more information on any of these terms!