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Core is a term used across fields to designate the central or most essential part of something, or the core components that define a system. The sense comes from the Latin cor, meaning heart, and it is used to describe both physical centers and foundational ideas.

In geology and geophysics, the Earth’s core consists of two parts: a liquid outer core and a solid inner core, predominantly iron with some nickel. The motion of liquid metal in the outer core generates the geomagnetic field through a dynamo process. The inner core remains solid under immense pressures. Seismic waves produced by earthquakes reveal the boundaries and properties of these layers, helping scientists infer composition and dynamics deep beneath the planet’s surface. Similar terminology is used for the cores of other planets and stars, reflecting regions where extreme conditions drive key processes.

In astronomy, the core of a star is the central region where nuclear fusion occurs. For the Sun, the core’s high temperatures and pressures fuse hydrogen into helium, releasing energy that makes the star shine. Energy then moves outward by radiation and convection.

In computing, a core refers to a processing unit within a central processing unit (CPU). Multicore processors, which contain multiple cores on a single chip, enable parallel execution and improved performance for modern software. The term also appears in older contexts, such as core memory (an early form of RAM) and occasional references to a program’s core components.

In mathematics and graph theory, the core of a structure denotes a minimal or essential substructure that preserves core properties of the whole, such as a graph’s core being a smallest subgraph that reflects its homomorphism behavior.