Adopted from http://www.tuxfiles.org/linuxhelp/fstab.html
Dump and fsck options. Well, dump is a backup utility and fsck is a filesystem check utility. I won't discuss them in great length here (they would both need their own tuXfile), but I'll mention them, because otherwise you'd spend the rest of the day wondering what on God's green Earth do these things mean.

the dump option. Dump checks it and uses the number to decide if a filesystem should be backed up. If it's zero, dump will ignore that filesystem. If you take a look at the example fstab, you'll notice that the 5th column is zero in most cases.

The fsck option. fsck looks at the number in the 6th column to determine in which order the filesystems should be checked. If it's zero, fsck won't check the filesystem.