vertical resolution 
The number of horizontal lines (or pixels) that can be resolved from the top of an image to the bottom. (Think of hundreds of horizontal lines or dots stacked on top of one another.) The vertical resolution of the analog NTSC TV standard is 525 lines. Some lines are used to carry other data such as closed-captioning text, test signals, and so on, so we end up with about 480 lines in the final image. All of the typical NTSC sources, including VHS VCRs, cable, and over-the-air broadcast TV (analog), non-HD digital satellite TV, DVD players, camcorders, and so forth, have a vertical resolution of 480 lines. DTV signals have vertical resolution that ranges from 480 lines for SDTV, to 720 or 1,080 lines for HDTV.