A Single-Lens Reflex (SLR) camera is a type of camera that uses a mirror and prism system to allow photographers to see exactly what the lens sees. When you look through the viewfinder, you are seeing the image that will be captured, which helps in composing the shot accurately. When the shutter button is pressed, the mirror flips up, allowing light to hit the image sensor or film. SLR cameras can be either digital or film-based. They are popular among both amateur and professional photographers due to their versatility and ability to change lenses. Many SLR cameras also offer manual controls, giving users more creative freedom in their photography.