Haito is often called the inner knife hand.
It indicates that you should strike with the opposite part of shuto. Haito uses a circular motion or a snapping action of the wrist depending on the distance and position. The circular motion is a strategic technique and surprising if combined with proper positioning.
See the images? That's 2 out of (arguably) 4 forms of Haito. They can all be used in different manners as well, which I cover in the video...
...and more down below in the trainingmethod and 2 Ippon Kumite as well.
The palm of the hand and can be used for attack as well as defence. You can find Shotei in Kata: