Is there any long-form, if at all? Or is it just a tradition from the 80's?
- run commands
- resource control
- run control
- runtime configuration
Personally, I'd go with run control, because ESR says so.
His footnote says:
The ‘rc’ suffix goes back to Unix's grandparent, CTSS. It had a command-script feature called "runcom". Early Unixes used ‘rc’ for the name of the operating system's boot script, as a tribute to CTSS runcom.
Wikipedia chooses "run commands" as the default long-form, but admits that context should determine word choice.
While not historically precise, rc may also be pronou- nced as "run control", because an rc file controls how a program runs. For instance, the editor Vim looks for and reads the contents of the .vimrc file to determine its initial configuration. The most sensible pronunci- ation depends on the function of the file: to start something up, or to control how something starts up.
According to this source -- http://kb.iu.edu/data/abdr.html -- it means "run commands"