Core

In biology, the core of a fruit contains its seeds.

In planetary science, the core of a planet contains its innermost layer(s). Due to planetary differentiation, such layers tend to be more dense than outer layers.

In a nuclear reactor, the core is the portion containing the fuel components.

In telecommunication, the term core has the following meanings:

1. The central region about the longitudinal axis of an optical fiber, which region supports guiding of the optical signal.

Note 1: For the fiber to guide the optical signal, the refractive index of the core must be slightly higher than that of the cladding.

Note 2: In different types of fibers, the core and core-cladding boundary function slightly differently in guiding the signal. Especially in single-mode fibers, a significant fraction of the energy in the bound mode travels in the cladding.

2. A piece of ferromagnetic material, usually toroidal in shape, used as a component in a computer memory device.

Note: The type of memory referred to has very limited application in today's computer environment. It has been largely replaced by semiconductor and other technologies.

3. The material at the center of an electromechanical relay or solenoid, about which the coil is wound.

In computer science, and in Unix and Unix-like operating systems, core is a file that contains a memory dump - known as a core dump (see above re magnetic core memory) - of a computer program that has crasheded for some reason. It is used for debugging purposes.

Myth

In Greek mythology, Core was an alternate term for Persephone.