A natural reflector is a tool (usually a building, or sidewalk) that will that will naturally reflect the sunlight for you. Traditionally, reflectors are big screens that have white, silver or even a gold backgrounds that can be used to reflect and direct light onto a particular spot. I personally don’t really use my reflector too often, but that is just my style. Instead of using a tradition reflector, I try to use natural reflectors.
If you have ever photographed a couple (or family) in the grass or around a lot of trees, you might notice that their clothes or skin color ended up with a green-ish tint. The sunlight is reflecting off of the green environment causing a green cast of color. Using a natural reflector allows for the sun to reflect off a white-ish background causing a perfect white balance for you without a reflector!
Sister Session at Christopher Newport University
Look for concrete areas that can naturally cast the sunlight for you. Boat ramps, columns, arches, walls, and even larger railings can all be used to naturally reflect the sunlight!
Consider areas that are completely enclosed with natural reflectors. The sunlight will bounce off all the walls and even the ceiling casting a more natural color. 
Kiana and Jacob’s CNU Wedding
Reflectors are tools that reflect (or bounce) the sunlight and they can be very useful. If you don’t have a reflector (or an assistant to hold an reflector) consider using a natural reflector to help you get an even and natural coloration.