There was a specification called MD DATA for this purpose, which could be used to store data in more ordinary way, however such discs could not be read by musical device, and had to be one of handful device specifically designed for this purpose -- while it was also used storing pictures from digital camera, as far as I know, it only showed limited use compared to MO as data medium. (Those MD DATA devices could also read musical media, but couldn't record them.)
Later in MD lifecycle, specification like Hi-MD did allow data featured storage class support (which you could write like 300MB of data to standard MD discs, and 1GB on Hi-MD media) this was very late in the MD lifecycle.
MiniDisc used as MO technology at its base, but it was definitely not used interchangeably, and MiniDisc was really specific media (mostly) used to music.