720p is lowest resolution of HDTV used by some cable providers and broadcast networks. "720" refers to the 720 horizontal lines of resolution (also known as 720 pixels of vertical resolution), while the letter "p" stands for progressive scan. This means that the entire image is displayed every 60th of a second. Each frame of 720p video has 1,280 pixels of width, and 720 pixels of height.
The general consensus is that progressive scan images will look a little better with fast motion (sports) but perhaps won't look quite as detailed on other content.
ABC, Fox, ESPN and a few others use 720p as their broadcast format. CBS, NBC, and most others use 1080i. In terms of bandwidth, 720p and 1080i are the same.