Horizontal resolution
From The Glossary of Digital Photography
The measurement of resolution in video in the horizontal axis. Different sources of video signals will have different resolutions (horizontal) that typically vary from 240 to 540 lines (or pixels) across the video image. The vertical resolution for analog sources is usually 480 lines at all horizontal resolutions. The resolution is determined by the number of lines that can be discerned and varies by source. See also resolution
