480p
480p is the shorthand name for a family of video display resolutions. The p stands for progressive scan, i.e. non-interlaced. The 480 denotes a vertical resolution of 480 pixels, usually with a horizontal resolution of 640 pixels and 4:3 aspect ratio or a horizontal resolution of 854 pixels for an approximate 16:9 aspect ratio. Since a pixel count must be a whole number, in Wide VGA displays it is generally rounded up to 854 to ensure inclusion of the entire image. The frames are displayed progressively as opposed to interlaced. 480p was used for many early plasma televisions. Standard definition has always been a 4:3 aspect ratio with a pixel resolution of at 60 Hz for NTSC regions, and 720 or for PAL regions. However, standard definition defines a 15.7k Hz horizontal scanrate, which means that interlacing has to be used for those resolution modes. The lowercase letter "p" in 480p stands for progressive, so the two must not be confused.
ATSC progressive mode standards
The ATSC digital television standards define 480p with 640×480p pixel resolutions, at 24, 30, or 60 frames per second.When 480p30 is broadcast on air, it is frame doubled then interlaced to 480i60. In case of 480p24, it is processed using the 3:2 pulldown technique to 480i60. In both cases the spatial resolution doesn't change, but the conversion to a interlaced format allows a direct digital to analog conversion for eventual broadcast on the analog television network.