What resolution?
Standard Definition TVs have 720 x 576 pixels, or 576 lines of 720 pixels.
High Definition TV screens have a lot more, starting with twice as many at 1280 x 720, and then up fivefold to 1920 x 1080 pixels, the more advanced you get.
So the more pixels, the better the resolution and the finer the detail you see in the images.
But what else makes HD give you such amazing picture quality? It’s the difference between a progressive and interlaced signal. Simply, the way the image is written and displayed on the screen.