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.