One of two types of shutter
for a camera
(see also, Focal Plane Shutter
A Leaf Shutter is located between the camera body and the attached lens. It works in a very similar fashion to the camera's aperture control device - overlapping leaves (usually metal, but sometimes plastic) set in a radial pattern rotate to create the desired size opening. This allows light to travel to the film plane evenly for the entire exposure duration. On some cameras the Leaf Shutter replaces the aperture device entirely.
For many photographers a Leaf Shutter is prefered over the older and more common Focal Plane Shutter because the shutter with the even exposure flash synch is available at all exposure speeds. Leaf Shutters also tend to be much less noisy and more reliable.