An Inverse Camera Angle is any camera angle obtained while holding Z/L that does not focus on Link's back. It is more difficult to perform in Majora's Mask than in Ocarina of Time, but it can still be useful in some places.
If done correctly, Link will be facing in the proper direction. This video shows some of the angles you can achieve:
Even if you're holding Z/L, some things (like a Spin Attack) will still return your camera to normal. Also note that if you didn't wait long enough in step 3 of the trick, you will end up with a quick turnaround.