It was originally called Star Gazing and recently also referred to as Twirling. The first time I ever witnessed Twirling first hand was in a Gouldian Finch. It is most common in Gouldians but it can effect other types of finches. No one can quite agree on what causes Twirling. It is either an infection, and injury, a genetic fault, or stress.
People think Twirling is basically the loss of the finch's equilibrium.
The finch will appear to be frantically looking around itself, like it is panicked. The head will tilt side to side and even roll upside down and back up. Twirling is also degenerative and the finch eventually dies. There is no treatment for this condition currently. Twirling is fatal because the finch eventually gets to the point it can not move without falling over.