There are a number of different forms of it.It is pretty much when you release an arrow before you consciously chose to.As soon as your pin comes close to what you are aiming at you punch the release,you can't get the pin to settle on the bullseye (freezing)an electric shock of adrenaline shoots through your body when you are about to shoot (flinching).It sucks big time!
It actually occurs more frequently with shooters who shoot a lot.When a shooter is more obsessed with hitting what they are aiming at versus their shot sequence and their form negative things can happen.
Having a disciplined shot sequence,relaxing,not being hesitant to let down if every thing isn't perfect,taking plenty of time between shots,making an effort to exagerate your follow through and hold on the area you were aiming at after you have released the arrow are all elements of consistently good shooting.
It's best to have these types of things in place to avoid ever having it! It almost had me give up archery many years ago.