.cd is the Internet country code top-level domain (ccTLD) for the Democratic Republic of Congo. It was created in 1997 as a replacement for the .zr (Zaire) ccTLD, which was phased out and eventually deleted in 2001.

A CD or compact disc is a thin plastic silvery disc for audio recordings.

The cd command, also known as chdir (change directory), is a command-line OS shell command used to change the current working directory in operating systems such as Unix, DOS, OS/2, AmigaOS (where if a bare path is given, cd is implied), Windows, and Linux. It is also available for use in shell scripts and batch files. The system call that effects the command in most operating systems is chdir(2) that is defined by POSIX.

Ceské dráhy (CD) or Czech Railways is the main railway operator in the Czech Republic. In 2014 its consolidated revenues reached CZK 33 billion. Revenues from passenger transport amounted to CZK 21 billion (64% transfer payments from the government, 25% intrastate transport, 11% international transport), revenues from freight transport operated by subsidiary CD Cargo amounted to CZK 12 billion. With twenty-four thousand employees CD Group is the fifth largest Czech company by the number of employees. The liabilities of CD Group increased from CZK 19 billion at the end of 2006 to CZK 51 billion at the end of 2014.

Compact disc (CD) is a digital optical disc data storage format. The format was originally developed to store and play only sound recordings but was later adapted for storage of data (CD-ROM). Several other formats were further derived from these, including write-once audio and data storage (CD-R), rewritable media (CD-RW), Video Compact Disc (VCD), Super Video Compact Disc (SVCD), Photo CD, PictureCD, CD-i, and Enhanced Music CD. Audio CDs and audio CD players have been commercially available since October 1982.