On an HDTV with "local contrast dimming", freeze frame at some point in a video where there's only a logo showing in the corner of the screen and the rest of the frame is black. (A screenshot of certain video game loading screens works, too.)

You will see that the area around the logo is glowing slightly, and that the area opposite the logo is completely lights out.

That is, essentially, the difference between "black" and "superblack". Both areas are displaying black, but one area is backlit and the other is not. Lit black is clearly different from Unlit black, because LCD pixels aren't perfectly opaque.

If you have an OLED TV (or an OLED phone, like a top-end iPhones), then every black pixel is superblack, which is why it looks so high contrast and gorgeous. If you have an LCD phone, you can see the "lit black" thing — but probably only if you set it next to an OLED phone.

Folks who know what "235" has to do with this, yes, I know, but I'm only addressing "what that might actually look like", not "deep dive into the RGB low/high problem". Feel free :)