Since the popularity increase of CB caps, I wish there were terms we could use here other than 'subsonic.'
To me and many other rimfire addicts, subsonic rounds have generally been used to refer to ammo in the 1000 to 1050 fps range with long rifle bullets (36 to 40 grains). Almost all target ammo fits in the catagory, as does some specialized hunting ammo (Ely subsonic hollow points, Lapua subsonic hollow points, Remington subsonic hollow points, etc). This ammo is quiet and extremely effective on small game right out to 100 yards or so, even with body shots.
The CB type ammo (29 grain bullets at 600 to 800 fps, even less if you look at some of the Aguilla stuff) is in a whole differenct catagory. Not even close to the previously mentioned stuff. Yes, it is subsonic but I wish we could just call them CBs instead. The bullets are lighter and they rarely, if ever, come with hollow points. They are much less effective on game. Will they work? Yep, but the ranges need to be much closer and the shots must be placed much better. While the subsonic 40 grain loads at 1000 to 1050 fps are among the most accurate rimfire loads ever made, the CBs rarely even come close.
Both have there place in the rimfire world. I shoot a huge number of both, but they are not even comparible other than the fact they are quieter than high velocity long rifles.
So I think it would be less confusing to call the quiet, accurate and effective 40 grain 1000 - 1050 long rifle stuff normal "subsonics", and the puny CB stuff "CBs."