Wiktionary
abbr. day, in two-digit, numeric format, as in: dd/mm/yyyy n. A Unix command for data transfer and modification. (rfex)
Wikipedia
DD, dd, or other variants may refer to:
dd is a command-line utility for Unix and Unix-like operating systems whose primary purpose is to convert and copy files.
On Unix, device drivers for hardware (such as hard disk drives) and special device files (such as /dev/zero and /dev/random) appear in the file system just like normal files; can also read and/or write from/to these files, provided that function is implemented in their respective driver. As a result, can be used for tasks such as backing up the boot sector of a hard drive, and obtaining a fixed amount of random data. The program can also perform conversions on the data as it is copied, including byte order swapping and conversion to and from the ASCII and EBCDIC text encodings.
The name is an allusion to the DD statement found in IBM's Job Control Language (JCL), in which the initials stand for "Data Description". The command's syntax resembles the JCL statement more than it does other Unix commands, so the syntax may have been a joke.
Originally intended to convert between ASCII and EBCDIC, first appeared in Version 5 Unix. The command is specified by IEEE Std 1003.1-2008, which is part of the Single UNIX Specification.
Usage examples of "dd".
DDS mounted, secured, and tested than it will to get the Archerfish up in the dry dock and back out again.
With the DDS secured to her back like a remora on a shark, the Archerfish stood out even among military ships.
Electrical power and compressed air and gas connections to the Archerfish also helped men inside the DDS conduct maintenance on the SDV.
Flooding the hangar chamber of the DDS changed the buoyancy of the Archerfish by several tons.