Similar to 1080p video, the “i” stands for “interlaced,” which differs from 1080p (progressive) video in that each frame contains two fields of data (but typically has double the frame rate). While progressive video is too large for broadcast, 1080i exists primarily for broadcast use, as the lower frame rate allows the signal to be sent over 60 Hz systems. The signal is 60i for NTSC or 50i for PAL.