A SLR camera, or Single-Lens Reflex 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 shots accurately. SLR cameras typically have interchangeable lenses, giving users the flexibility to choose different focal lengths and styles for various photography needs. They are popular among both amateur and professional photographers for their image quality and control over settings like aperture and shutter speed.