The X Resolution is a form of metadata that can be found in multiple files. This includes images, videos and all kinds of files with a visual representation. The X Resolution refers to the resolution of the visual part of a file, yet only to the resolution of the x-axis.
The x-axis is also known as the horizontal or principal axis in a coordinate system. With respect to files, this means that the X Resolution refers to the horizontal resolution of an image or visual data of a video or other file.
Usually, the X Resolution is represented by using pixels. In some cases, however, the value could also be measured in centimeters (cm) or millimeters (mm).