/etc/fstab is the filesystem table. /dev/… or UUID=…)
none, for example for swap partitions)
/dev/sda5 none swap sw 0 0 /dev/sda6 / ext4 rw,relatime,data=ordered 0 1 /dev/sda7 /var ext4 rw,relatime,data=ordered 0 2
mount -a mounts all filesystems mentioned in /etc/fstab. mount -a [-t fs-type] [-O optlist]
mount -a with -F to make mount fork so that filesystems are mounted in parallel. genfstab helps to create an initial /etc/fstab file when a system is installed.