Disk and disc have very similar pronounciation, but they are very different: 2 alternative spelling for things that are generally thing and circular geometry. For the most part the words "disc" and "disk" can be used interchangeably to describe these flat, rounded objects. The terms and the objects appear in fields such as computers, media where id=science, anatomy and automotive mechanics. Some of these fields primarily use one spelling, others use both, depending on the specific object. In many fields the spellings can be used interchangeably, but generally in computer technology the word disk refers to the magnetic storage (hard disks, floppy disks or diskettes) while disc refers to optical storage (compact discs or CDs, digital versatile discs or DVDs).
In computers and media these 2 words refer to storage devices for data, music and videos. You can store all kind of files on them, but the difference in their structure give you different ways to write, organize and read the data from them.
Disks are always rewritable unless intentionally locked or write-protected, the user can easily partition a disk into several smaller volumes.
Phonographic records were also known as discs in the old times, people who played records on radio stations were called disc jockeys. When the optical storage devices were introduced this spelling carried over into compact discs (CDs and CD-ROMs) and digital versatile discs (DVDs, DVD-ROMs, DVD-RAM and DVD-Video discs). Some discs are read-only (ROM), others allow the users to burn the content (write files using lasers) to the disc once, some can be erased and rewritten over many times (such as CD-RW, DVD-RW, and DVD-RAM discs).
In astronomy the shape of a galaxy might be described as a disc. A ring of debris orbiting an object such as a star, on the other hand, typically is referred to as a debris disk.
Anatomical objects typically use the "disc" spelling. For example, a medical doctor refers to a "herniated disc" when a patient has a certain injury to the fibrocartilage between vertebrae in the spine or he talkas about optic discs in the eyes and plancental discs in females.
In automotive mechanics a disc brake is the device that uses friction against a circular metal plate to slow or stop the vehicle's wheel.