I can clarify some of the tech stuff.

A “disk” is a concept. It’s an object which contains data.

“Hard” disks and “floppy” disks are always referring to the rigidity of the internal storage media. 7", 5.25", and 3.5" floppy disks have the same round magnetic storage material. The only difference with a 3.5" floppy disk is that they put a hard case over the floppy disk.

CD, DVD, Blu-ray, etc are both disks and discs, as their typically handled without a caddy/case. So technically both apply.

SSDs are still disks, just solid state, rather than floppy/hard spinning magnetic media.

Technically flash drives are also solid state disks, but we don’t generally conflate the two terms for clarity.