And even before that, it was used to describe bulk audio tape that would then be spooled onto individual reels.
As for Betacam, I believe that the “official” designation of large and small cassetes is simply “L” and “S”. Large and small? could it be that simple?
At least that’s how the tapes used to be named when ordering them. In Sony’s service manuals the two cassette sizes are always referred to as S and L.
My 2