When installing new software using yum, you will occasionally get the the option of “Is this ok [y/d/N]:” Everyone knows recognizes Yes and No, but the option d may have thrown you for a loop.
“d” simply stands for download only. If you were to do this from the commandline you’d use this:
Occasionally this is useful if you are prepping a resource, like a thumb drive, with all of the RPMs that you standardly install. You might also want to have the RPMs available for switching between versions of software. I’m sure there are many more reasons too.
Hopefully this has answered your question.