The "i" and the "p" that follow the format designation have specific meanings. In the "i" or Interlaced Format, "p" stands for Progressive Format.
The progressive scan (p) format is an alternative to interlaced video that improves the overall picture quality on larger screens. Progressive scanning combines 480 unique lines of picture information into one picture frame and corrects picture quality automatically. It treats the entire video image as one frame. Progressive scanning reduces jagged pictures and smoothes movement on larger monitors. For standard-definition television, this resolution is known as 480p. In addition, progressive scanning provides motion handling that is as good as the interlaced format.