Unix/Lunix Filesystem Hierarchy Standard

The Filesystem Hierarchy Standard is a set of guidelines designed to get various distrobutions of Linux/Unix all on the same page with regards to what goes where in the file system.

For us laymen, it's a decent guide to what is where in the filesystem (why is there a /sbin and a /usr/local/sbin?). It helps answer questions like, "If I have a backup script, where should I put the file?".