HDTV means high-definition television
HDTV is television with a much higher (up to 1920×1080) resolution than normal TV (often called SD). With an HDTV, you can see grass feelers on a football field sharply, with a normal television you see just grass. If you have an HDTV you don't want to say that everything is sharp. Of course you have to watch something that is also HD at that moment. If the transmitter broadcasts an old movie, then that is still SD (standard definition). A classic TV image is analogous and has a size of 4:3, with HDTV being 16:9. The image of HDTV gives much more detail, is not vibrating and also gives a sharper picture. Upscalen is also often used in broadcasting television material: This means that the image has been converted to HD. This is not the same quality as true HD, but better than normal classic image. Nowadays, there is also ultra-HD 4k. This is even better and sharper than the known HD.