HD stands for High Definition, while UHD stands for Ultra High Definition. HD refers to a display resolution of 1920×1080, while UHD refers to a display resolution of 3840×2160. HD offers a sharper picture than standard definition, while UHD offers a much sharper picture than HD. UHD also offers more pixels per inch, meaning that the picture will be much clearer than HD. UHD also offers a wider range of colours, which further enhances its picture quality. In addition to this, UHD also offers higher refresh rates, making it better for gaming and other activities that require quick response times.