You mean the height? The "p" alone stands for progressive scan, which means all rows are rendered in order. The other option is "i", meaning interlacing, which means all odd and all even are rendered separately, then interlaced together. Interlacing can cause some flickering problems, and was really only used because it was lighter on the data sent. Pretty much all modern displays use progressive scan. In 1024x768, that is x*y, or width (number of columns) by height (number of rows).
