480i is the shorthand name for a video mode, namely the US 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 483 of these are used to display the image for DV-NTSC. Its PAL/SECAM counterpart is 576i; together, these are the two common forms of standard-definition television.

For analog NTSC there is a total of 525 scanning lines of which originally 483 lines were visible (241.5 visible lines + 21 lines of vertical blanking per field) and later 480 (240 complete lines per field). A full frame is split into even and odd fields where the even fields end with half a line and the odd fields begin with the other half of the line. By convention an NTSC video frame is considered to start with an even field followed by an odd field. The disparity of the line numbering compared to other systems is solved by defining the line numbering to start five equalising pulses (or 2 and a half lines) earlier than on all other systems (including Systems A and E even though they had no equalising pulses) on the first equalising pulse following an active line or half line. This has the effect of placing a half line of video at the end of the even (first) field and the beginning of the odd (second field). Thus the line numbers correspond to the real lines of the video frame. On all other systems, the field was considered to start with the falling edge of the first field pulse which gave the confusing position that the odd field (first) had a half a line of video occupying the latter half of a whole line and ended with a whole line of video but half a scanning line (and vice versa for the even field). The NTSC convention solved this confusion.