In most (all?) *nix systems there's a directory named
/etc, what does etc stand for?
It stands for "et cetera" that means in Latin "and other things"
From the Wikipedia:
There has been controversy over the meaning of the name, but in early versions of the UNIX Implementation Document from Bell labs, the section for /etc is clearly commented as etcetra directory, as this directory historically held everything that did not belong elsewhere (though in FHS it is clearly restricted to static configuration files and may not contain binaries)
Et cetera (in English contexts pronounced /ɛtˈsɛtərə/) is a Latin expression that means "and other things", or "and so forth". It is taken directly from the Latin expression which literally means "and the rest (of such things)" and is a loan-translation of the Greek "καὶ τὰ ἕτερα" (kai ta hetera; "and the other things". The more usual Greek form is "καἱ τἁ λοιπἀ": "and the remainder"). Et means "and"; cētera means "the rest".
Obviously the actual meaning of "etc." aka "et cetera" has been explained above, however to explain more in relation to *nix...
It was intended to be where the miscellaneous files are stored which don't fit into the "categories" of the other root directories, however it has ended up being used mostly for system configuration.
A quick Google search turned up this discussion on your very question. Looks like the jury's undecided, but it's probably "et cetera."
Another hypothesis is that it's named after "editable text configuration", and I tend to find this a more suitable explanation even if not correct.