From The TV IV
720p is the name given to a specific HDTV video mode. The number 720 stands for 720 lines of vertical resolution, while the letter p stands for progressive scan or non-interlaced. It is currently the highest quality progressive scan video mode available for HDTV, although the 1080p format is currently being developed, which will supersede 720p. The 720p format is excellent for showing high speed action and sports broadcasts, due to the fact that it is progressive scan. 720p is the format used by ABC and FOX for their standard HDTV broadcasts.
720p resolution is 1280 × 720.