480i is the shorthand name for a video mode, namely the U.S. NTSC television system or digital television systems with the same characteristics. The i, which is sometimes uppercase, stands for interlaced, the 480 for a vertical frame resolution of 480 lines containing picture information; while NTSC has a total of 525 lines, only 480 of these are used to display the image. The digitally transmitted horizontal resolution is usually 720 or 704 pixels with an aspect ratio of 4:3 and therefore a display resolution of 640 × 480 (VGA); that is standard-definition television (SDTV).    
The field rate (not the frame rate) is usually (60/100.1% ≈) 59.94 hertz for color TV and can be rounded up to 60 Hz. There are several conventions for written shorthands for the combination of resolution and rate: 480i60, 480i/60 (EBU) and 480/60i. 480i is usually used in countries that conventionally use NTSC (most of the Americas and Japan), because the 525 transmitted lines at 60 hertz of analogue NTSC contain 480 visible ones.