A syntactically correct line of /etc/fstab must have six fields, separated by whitespaces or tabs. The fields are as follows:
The device file, UUID or label or other means of locating the partition or data source.
The mount point, which is the directory where the device is/will be mounted.
The file system type, which specifies the type of the file system.
The mount options, which are a comma-separated list of options that control how the file system is mounted and accessed.
The dump flag, which is a number that indicates whether the file system should be backed up by the dump utility. This is an outdated method and should not be used.
The fsck order, which is a number that indicates the order in which the file system should be checked by the fsck utility at boot time. A value of 0 means no check, a value of 1 means the root file system, and a value of 2 or higher means other file systems.
For example, a line of /etc/fstab could look like this:
UUID=80b496fa-ce2d-4dcf-9afc-bcaa731a67f1 /mnt/example ext4 defaults 0 2
This means that the file system with the UUID 80b496fa-ce2d-4dcf-9afc-bcaa731a67f1 is mounted on /mnt/example, has the type ext4, uses the default mount options, is not backed up by dump, and is checked by fsck after the root file system.
References:
How fstab works - introduction to the /etc/fstab file on Linux
/etc/fstab - Gentoo wiki
fstab(5) - Linux manual page
/etc/fstab file | Linux# - Geek University
