According to GC28-6704-1, IBM System/360 Operating System: Job Control Language Reference,

DD means "Data Definition". Bitsavers knows all.

On Sun, Sep 15, 2024 at 10:15 PM Dave Horsfall <dave@horsfall.org> wrote:

On Mon, 16 Sep 2024, Rob Pike wrote:

[ The origin of the "dd" command ]

> I was told it's IBMese: Define Dataset.

Straight from IBM's JCL (Job Control Language); heck, I still remember
obscure things like "DISP=(,KEEP)" etc...

-- Dave