What is indicated by the term 'igneous' rock?

The term 'igneous' rock refers specifically to rock that has formed from the cooling and solidification of molten material, known as magma or lava. When molten rock cools, it crystallizes, and this process creates the various types of igneous rock. Igneous rocks can be classified into two main categories based on where they cool: intrusive (or plutonic) rocks cool slowly beneath the Earth's surface, allowing larger crystals to form, while extrusive (or volcanic) rocks cool quickly at the Earth’s surface, resulting in smaller crystals.

The other choices refer to different types of rock formation. The transformation of rock by heat and pressure pertains to metamorphic rocks, whereas sedimentary rocks form from the accumulation and lithification of sediments. The statement about being primarily composed of crystals can apply to a variety of rock types, including some igneous rocks, but it is not specific enough to define 'igneous.' Thus, the focus on cooling from molten magma is what makes the definition of igneous rock precise and accurate.