Ground Jumps allow you to perform a vertical jump to gain extra height. This is particularly useful for getting to those just out of reach ledges. Storing a ground jump also allows you to skip Navi & the Owl's text triggers.
There are a few ways to store a ground jump:
Afterwards you can release Z and R and if the glitch worked, you should not be able to pull out your sword or any C-items.
Backflipping or Sidehopping will activate the glitch and cause you to jump straight up.
It is also possible to store a ground jump with the Explosive Limit as shown in the video.
This method is pretty rare to use due to its difficulty and the time it takes to store the ground jump, but this is the only way to ground jump during a hover.