A pastry wheel is a device to cut out rolled pastry.
It consists of a cutting wheel attached to a handle. The wheel will have a straight, sharp edge. The wheels come in different sizes. Some are small for fine work, some are large enough to slice cooked pizza.
A pastry wheel is different from a pastry jigger in that while the primary purpose of a pastry wheel is to cut, the primary purpose of a pastry jigger is to decorate.
The functionality of the two devices is often, however, combined, leading to cutting wheels with jagged edges that both cut and decorate pastry at the same time.
Technically, if there is a decorative edge, then the device is a pastry jigger, but that term is being conflated now into pastry wheel.
Some pastry wheels have interchangeable wheels, including a plain edge and some jigging edges. Others have dual wheels attached to the handle: a plain edge wheel to the left, a decorative edge wheel to the right. Which one you use depends on how you turn and angle the device.
See also: Pastry jigger, Pastry Frame, Pastry Frames, Pastry Cloth Pad, Pastry Cloth, Pastry Blender, Pastry Brush