Save the current menu entry or num if specified as a default entry. Here is an example:

          default saved
          timeout 10
          
          title GNU/Linux
          root (hd0,0)
          kernel /boot/vmlinuz root=/dev/sda1 vga=ext
          initrd /boot/initrd
          savedefault
          
          title FreeBSD
          root (hd0,a)
          kernel /boot/loader
          savedefault
     

With this configuration, GRUB will choose the entry booted previously as the default entry.

You can specify `fallback' instead of a number. Then, next fallback entry is saved. Next fallback entry is chosen from fallback entries. Normally, this will be the first entry in fallback ones.

See also default and Invoking grub-set-default.