The Image Height is one part of the information that determines a picture's, photo's or other image's dimension. Together with the image width, this value determines the size of an image itself, not the file size.
Often, Image Height is given in pixels, e.g. 682 px. However, most programs are also able to tell the height of an image using other values like inches, mm or cm. Converting the Image Height from pixel to inch, however, can cause discrepancies, because the pixel value oftentimes cannot be 100% translated into another value.
It is important to know the height of an image, especially when you plan to print, upload or embed the image in a document, video or website. When uploading, not only file size restrictions with regard to MB come into account, but also the actual size of an image. Likewise, it's important to know both the width and height of an image, to embed it in a video without black bars appearing on the sides or top and bottom.