SLR stands for “Single Lens Reflex,” a camera design where a single lens is used for both viewing and capturing images. In SLRs, light passes through the lens and is reflected by a mirror into a viewfinder, ensuring that what the photographer sees matches the captured image. When the shutter is pressed, the mirror flips up, allowing light to hit the sensor (in digital SLRs) or film. This design offers precise composition and focus. While SLRs can be digital (DSLRs) or film-based, newer mirrorless cameras have become popular, offering similar benefits without the reflex mirror, resulting in a more compact form.