Disc

Disc is a flat, circular object bounded by a circumference. The term is used across many fields to describe round, planar shapes. In American English the spelling disk is common; disc is typically used in British English and in scientific terms. The two spellings are often interchangeable for non-technical uses.

In geometry, a disc refers to the filled circle, including interior points, as opposed to the circumference only. The area is πr^2, and the circumference is 2πr.

In anatomy, an intervertebral disc cushions adjacent vertebrae in the spine. It consists of an outer ring called the annulus fibrosus and an inner gel-like core called the nucleus pulposus. Discs can degenerate or herniate, causing back pain and neurologic symptoms.

In information technology and media, optical discs store digital data as pits and lands read by a laser. Common formats include CD (compact disc), DVD, and Blu-ray. Capacities vary: about 700 MB for a CD, 4.7 GB for a single-layer DVD, and 25 GB for a single-layer Blu-ray (up to 50 GB dual-layer). Rewritable versions exist (CD-RW, DVD-RW).

In engineering, discs serve as brake rotors, flywheels, or clutches. They are flat, circular components made of metal or composite materials designed to transmit torque, store energy, or convert kinetic energy.

In astronomy, accretion discs and protoplanetary discs are rotating structures of gas and dust surrounding a central object such as a young star or black hole. These discs play a key role in angular momentum redistribution and planet formation.

In sports and recreation, a disc (often called a Frisbee) is a handheld flying disc used in games such as disc golf and ultimate.