SLR - Single Lens Reflex
SLR utilizes an automatic moving mirror system which enables the photographer to see exactly what will be captured by the film or digital imaging system. It basically uses a mirror and prism system to see exactly what will be captured.
Merit & Demerit - The main advantage of an SLR camera over others is that, you can change the lenses to get the desired image. But, a Single Lens Reflex Camera is more heavier and costs more as compared to point-and-shoots camera.