Well, I've noticed a lot of these popping up in Slayer, Pantera, and other metal tab.
I have no idea what the difference betwen these and normal harmonics is, though.
Pinch harmonics (also called pick harmonics, or in country music ckicken picking). hold your pick further up in your hand, so just the very bottom of the pick is is exposed. as you pick down on the string the side of your thumb should barely touch the string that you are playing, which will sound the harmonic. You might have to rotate your wrist to get your thumb to do this. It takes some practice, but it is an easy effect to master. It also works great when bending strings.
Let me know if this helps, pm me if you have any questions.