What is the term for igneous rock that cools and solidifies beneath the earth's surface?

The term for igneous rock that cools and solidifies beneath the Earth's surface is intrusive rock. This type of rock forms from magma that cools slowly underground, allowing the growth of large crystals, which is a characteristic feature of intrusive rocks.

Intrusive rocks, also known as plutonic rocks, contrast with extrusive rocks, which form from lava that cools quickly on the Earth's surface, leading to a different texture, generally with finer crystals. Rhyolite and basalt are specific types of extrusive rocks, named based on their mineral content and texture rather than their formation location. Therefore, in the context of the question, intrusive rock accurately captures the process and conditions of formation beneath the Earth's surface.