Core can be a noun, verb, or adjective, but is most often used as a noun to refer to the central or most important part of something (“the core of the issue,” “the Earth’s core”) or to the usually …

The core of a nuclear reactor (= a device in which atoms are changed to produce energy) is the place where fission (= the dividing of atoms) happens.

The core is made primarily of iron and nickel and has two parts — an inner solid core and an outer liquid core. The mantle is the layer of the Earth that overlies the core.

Earth's inner core is the innermost geologic layer of the planet Earth. It is primarily a solid ball with a radius of about 1,230 km (760 mi), which is about 20% of Earth's radius or 70% of the Moon …

Of basic importance; essential: "Virtually all cultures around the world use the word heart to describe anything that is core, central, or foundational" (Robert A. Emmons).

Aug 10, 2025 · "Core" represents centrality, importance, and functionality across various domains. Whether describing a fruit, a principle, or a technical component, its meanings emphasize its …

CORE meaning: 1 : the central part of a fruit (such as an apple) that contains the seeds; 2 : the central part of something

Definition of core noun in Oxford Advanced American Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more.

So the core of something is its very heart, whether you're talking about the seed-containing center of a fruit, the central meaning of a book, or the core courses you need to take in order to …

The core of something such as a problem or an issue is the part of it that has to be understood or accepted before the whole thing can be understood or dealt with.