For the most part, the words "disc" and "disk" can be used interchangeably to describe flat, rounded objects. The British tend to prefer "disc," and Americans generally use "disk" as their default spelling. In some cases, the spelling with a "k" at the end is based on Germanic origins, and the spelling with a "c" at the end is based on Greek or Latin origins. The use of "disc" or "disk," however, is often simply a matter of preference within a particular field of use. No matter the field or the typical spelling for a particular object, it is not unusual to see the other spelling used, even by respected sources.
The word "disk" entered the popular vernacular first, sometime during the 17th century. By the 18th century, however, there was a movement toward incorporating Latin roots whenever possible. The Latin word discus led to the use of "disc" to refer to thin, circular objects.
Discs or disks appear in fields such as computers, media, science, anatomy and automotive mechanics. Some of these fields primarily use one spelling, and others use both, depending on the specific object. In many fields, the spellings can be used interchangeably.
In computers and media, "discs" or "disks" typically refer to storage devices for data, music and videos. Phonographic records were also known as discs, and people who played records on radio stations were called disc jockeys. When optical storage devices were introduced, this spelling carried over into compact discs (CDs) and digital versatile discs (DVDs). Magnetic storage devices often use the spelling with a "k," as seen in floppy disks and computer hard disks.
Anatomical objects typically use the "disc" spelling. For example, a healthcare professional might refer to a "herniated disc" when a patient has a certain injury to the fibrocartilage between vertebrae in the spine. Other discs in the human body include optic discs in the eyes and placental discs in females.
In automotive mechanics, a disc brake is a device that uses friction against a circular metal plate to slow or stop the vehicle's wheel. 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.