An HD (High Definition) television is one that has a resolution of 1280x720 pixels. It offers picture quality above standard definition (SD), but it is not the highest available.
HD-Ready also refers to televisions capable of handling a high-definition signal, usually with a minimum resolution of 720p (1280x720 pixels). The "HD-Ready" label indicates that the TV can display HD content, but does not necessarily output it natively; That is, it can receive and display an HD signal, but it does not have to have a native HD resolution. It is often associated with televisions that are HD-ready but do not include a built-in high-definition digital television tuner.
Full HD, on the other hand, refers to a resolution of 1920x1080 pixels. This resolution offers a more detailed and clear image than standard HD or HD-Ready, with twice as many pixels in total. Full HD TVs can display content in 1080p natively, meaning the picture is produced at the highest standard HD resolution, offering a richer and more detailed viewing experience.
It doesn't have to, many televisions sold about 10 years ago have the name HD in their name and label, although it does not mean that they have an HD tuner, that is, they are not capable of understanding and emitting the high definition signal that they receive over the cable. antenna.
You can obtain more information in this article: Goodbye to the SD era: the DTT blackout and how to continue enjoying your TV.