From LQWiki

/etc is the home of most core configuration files in linux. It has details and preferences related to hardware, run levels and just about everything that comes with a barebones kernel install.

Important files in /etc:

• fstab
• group
• hosts
• modules.conf
• network/interfaces
• passwd
• shadow

Obsolete and not likely to be seen any more (as of 2011)

• grub.conf (legacy GRUB only)
• hostname
• inittab (SYSV init)
• lilo.conf (LILO only)