How to define a SLR camera?

Digital SLR camera is a single lens reflex digital camera, referred to as SLR (single lens reflex). This technology is to install a mirror at a 45 angle in front of the film plane, and there are frosted glass and pentaprism eyepiece above the mirror in turn. The pentaprism reflects the real image light many times to change the optical path, and sends the image to the eyepiece, so that the image seen in the observation window is always consistent with the image on the film, and the shooting range is basically the same as the actual shooting range. The unique design of this prism enables the photographer to directly observe the image passing through the lens from the viewfinder.