One of the resolution specs used in the HDTV. 1080i stands for resolution of 1920x1080 pixels and the magic little 'i' means that the video is being interlaced.

Other common HDTV resolutions are 720i and 720p.

The number 1080 itself stands for 1080 lines of vertical resolution and the term implies a widescreen aspect ratio of 16:9.