A peeling knife is basically a paring knife
, with a curved, slightly more flexible, blade
. The blade is short (2-4 inches) and has a concave curve along it's sharp edge, which is why it's sometimes called a bird beak knife - the upper, blunt edge of the blade may be curved too, for aesthetic effect.
The curvature of the blade makes it more useful for - yes! - peeling things, because the things you peel tend to be curved as well. As with a paring knife, the handle should provide a very secure grip, because you are most likely going to be holding the peeled object in your other hand, and working close in. A slippy one of these is probably worse than useless, and you shouldn't bother with it.