The "i" and the "p" that follow the format designation have specific meanings. In the "i" or Interlaced Format, "p" stands for Progressive Format.
In Interlaced format pictures are first drawn using the odd numbered resolution lines (1, 3, 5, etc.) followed by the even numbered lines (2, 4, 6, etc.). Thus, there are two fields (odd and even) drawn on the monitor for each frame. This scheme is referred to as interlaced video and commonly operates at rates of 50 or 60 fields per second. This odd/even drawing pattern is calledinterlacing (i), and was developed to improve picture quality without increasing transmission bandwidth (the data rate capacity of a given network connection).