1080i is the shortened name for a combination of frame resolution and scan type, in the domains of high-definition television and high-definition video. The term 1080i assumes a display aspect ratio of 16:9 (widescreen), implying a frame resolution of 1920 pixels wide by 1080 pixels high (1920×1080). The i stands for interlaced scan. A frame of 1080i video consists of two fields which resolve to 1920×540 pixels each, and whose horizontal lines are intertwined (that is, interlaced). 1080i differs from 1080p, in which the p stands for progressive scan.

In native or pure 1080i, the two fields of a frame correspond to different instants (points in time). This is true for interlaced video in general and can be easily observed in still images taken from fast motion scenes, as shown in the figure on the right. However, when, for processing or broadcasting purposes, 1080p material at 25 or 30 frames/second is converted to 1080i at 50 or 60 fields/second, respectively, both fields in a frame do correspond to the same instant. The field-to-instant relation is somewhat more complex for the case of 1080p at 24 frames/second converted to 1080i at 60 fields/second, as explained in the Telecine article.