What Does Quad HD (QHD) Mean?
Quad HD is a resolution convention used in high-end display systems such as LED TVs, monitors and smartphones. With four times the resolution of HD or "HD Ready" (720p), QHD is specified as 2560×1440 pixels at a 16:9 aspect ratio. Ultra-wide QHD enhances the horizontal pixels to 3440 for a 21:9 aspect ratio.
Techopedia Explains Quad HD (QHD)
QHD has a resolution of 1440p, where 1440 is the pixel value and p stands for progressive scan or non-interlaced. Because of its high resolution quality, QHD is more suitable for large screens as it has such high pixel density. On tablets and smartphones where screens are smaller, the pixel density of QHD goes up to 538 dpi. Quad HD should not be confused with qHD (quarter HD), whose resolution is one-quarter of 1080p's at 1980×1080.