It means "et cetera". In Latin literally "and the rest". And I have proof.
Edit: In an archived postThe original link above, dated March 43, 2007, has been archived. In it Peter H. Salus quotes an email he "just received" from Dennis Richie, co-creator of Unix, making very clear what "etc" initially stood for:
I assure you that the original contents of /etc were the "et cetera" that didn't seem to fit elsewhere. Other variants might do their own etymologies differently.
Regards,
Dennis