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What does the .d stand for in directory names?
Consider that we have (on many sytems) init.d that contains executable scripts and symbolic links for run levels, sysctl.d that contains text configuration files for kernel tuning on boot and modprobe.d that contains text configuration files to load kernel modules on boot. These are just examples.
What, precisely is the similarity between the contents of these locations that necessitates the .d suffix on the end of the directory? What would be an inappropriate use of it?
I've been using UNIX like operating systems for well over 15 years, and I found that I could not explain the significance of .d to someone today.
Addendum:
I thought it signified 'daemon', but neither modprobe nor sysctl would fit in that category.
