It's a device where distance to the display, resolution and screen size are such that someone with normal vision cannot distinguish between pixels.
It is a post-development sales pitch used to pitch as a differentiation the fact that Apple's naive scaling required them to grossly overshoot the mark. Competitive products already had excellent displays before Apple decided that they had no choice but catch up.
I would love it if any company could call their HD TVs retina displays
Why would you love it? "Retina" display is a misnomer -- unless the device is a fixed distance from my eyes, and it is specifically geared for my eyes specifically, it is horse shit to call it a retina display. It is ignorant marketbabble that lowers us all.