They mean specifically High-Definition television, which means an image 1920x1080 pixels, like the released image. As a milestone, it's better compared to the Apollo-era analog TV cameras that went to the Moon, which used North American commercial TV standards of around 535x400. HDTV is much better than that.

"High definition" in TV is nothing much compared to "high resolution" in still imagery. Jacob's right that chemical film has a much higher resolution (and more accurate color). Galileo looked back and took some stills of the Earth-Moon system that have been assembled into a nice high-res image. Kaguya, I'm afraid, doesn't come close to the record for still image resolution.

Still, nice pic. I don't think it's possible to take a bad picture of the Earth from space.