A giant drill used to bore into mountains is typically called a tunnel boring machine (TBM).

Here's why:

* "Tunnel": TBMs are specifically designed for creating tunnels, not just drilling holes.

* "Boring": This term refers to the process of excavating a tunnel by rotating a cutting head and removing the excavated material.

* "Machine": TBMs are complex, powerful pieces of machinery.

While "drill" might be used in casual conversation, it's not the most accurate term for a machine that creates tunnels.