Famicom Disk System; FDS
A peripheral for the Nintendo Famicom that used proprietary floppy disks. Often abbreviated as FDS. The two senses refer to the same product; the second is simply an abbreviation.
The Disk System was a peripheral for the Famicom.
Back then, Disk System games could be rewritten.
From English 'disk system', referring to the floppy-disk-based add-on for the Nintendo Famicom.