Disk vs. Disc
In the US, the correct spelling for a flat circular object is "disk".
The British/European spelling is traditionally "disc". So if you spell "color" as "colour", then you probably also use "disc".
Additionally, the spelling "disc" has found its way in to various technical jargon.
A computer 8", 5.25", or 3.5" floppy disk is always spelled "disk". Sometimes the term "diskette" is also used.
Notoriously when the Japanese company Sony released their optical DISK media, they stylized the product branding as "Compact Disc". This is a trademarked name, and refers to both their original product, and any compatible products that adhere to the same specification.
To reduce confusion, it is recommended to abbreviate as CD or CD-ROM.
