Resolution: The sharpness of a video image, signal or display, generally described either in terms of "lines of resolution," or pixels. The resolution depends on two factors: the resolution of the display (Native) and the resolution of the video signal. Since video images are always rectangle-shaped, there is both horizontal resolution and vertical resolution to consider.
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. But, some lines are used to carry other data like closed-captioning text, test signals, etc., so we end up with about 480 lines in the final image, regardless of the source. So, all of the typical NTSC sources - VHS VCRs, cable and over-the-air broadcast TV (analog), non-HD digital satellite TV, DVD players, camcorders, etc. - have vertical resolution of 480 lines. DTV (Digital Television) signals have vertical resolution that ranges from 480 lines for SDTV, to 720 or 1080 lines for true HDTV.
Horizontal resolution: The number of vertical lines (or pixels) that can be resolved from one side of an image to the other. Horizontal resolution is a trickier concept, because while the vertical resolution of all analog (NTSC) video sources is the same (480 lines), the horizontal resolution varies according to the source. Some examples for typical sources: VHS VCRs (240 lines), analog TV broadcasts (330 lines), non-HDTV digital satellite TV (up to 380 lines), and DVD players (540 lines). DTV signals have horizontal resolution that ranges from 640 lines for SDTV, to 1280 lines (for 720p HDTV) or 1920 lines (for 1080i HDTV).