" A D-SLR is a digital camera that uses a mechanical mirror system and pentraprism to direct light from the lens to an optical viewfinder at the back of the camera."
In layman's terms, simply because I don't quite get all the inner workings of a D-SLR itself, personally I'd describe it is a high resolution digital camera with more options like setting the lens aperture and shutter speed, as well as usually viewing your subject through an optical viewfinder instead of an LCD one. This also allows it to have real time changes made without and lag time at all, unlike some digital cameras on the market. But enough with all the technical info.
I've obtained a D-SLR camera from my dad, who had just gotten a new one and decided that I could have his old one. Although I can't take video with the D-SLR he gave me, it allows me to take professional level photographs already. Below are a couple experiments of pictures as I played around with the D-SLR on my free time.