Regarding how many p's on a cell phone screen e.g. 720p 1080p with a resolution of 1280 x 800 pixels is it the 800 at the end that is looked at to differentiate the p's?

p is progressive scan, meaning progressive scan.

All screens are actually made up of small dots, which are called pixels. The number of dots in the horizontal and vertical directions of a square screen is multiplied by the number of pixels in the screen (the pixels in a digital camera are also multiplied by the number of pixels in a digital camera).

But to make it easier to express the size of the screen, it is usually expressed as horizontal pixels x vertical pixels, such as 1024 x 768 pixels, which is common for computer screens, and 240 x 320 pixels, which is common for cell phone screens.

Expanded Information

4:3, 16:9, 16:10, 21:9 These ratios are in fact the ratio of horizontal to vertical pixels in the resolution. 4:3 is the original resolution size ratio we use, the previous computer screen is almost always 4:3; then the emergence of wide-screen monitors, 16:10 began to be popular. popular, and the more common resolutions are 1280 x 800 pixels.

Then later with the development of HDTV, 16:9 this size resolution also began to promote, because HDTV sources are usually 1080p and 720p (1280 × 720 pixels), because the traditional 16:10 display device to watch high-definition will be left with black edges, and 16:9 size display device can be realized without black edges of the playback, which is this kind of FULL HD display devices are popular.

Reference:

Baidu Encyclopedia - Cell Phone Screen Resolution