In 1936, the BBC introduced its viewers to high-definition TV. (Well, that's what they called it, anyway.) The Beeb's new broadcast system produced a blurry, black-and-white 405-line image. Still, it was a lot better than the 30-line standard it replaced. Seventy years later, the name's the same; only the specs are different.
The screen at your local movie theater is obviously a lot larger than the specialty screens used in home theaters, but they actually have a lot in common. The main difference is perforation. The screens in almost every movie theater have the front left, center, and right speakers behind them, along with a few subwoofers.