I have some experience with ND filters and thought this would be a good opportunity to give you a little more detail. A neutral density filter is a glass filter that fits to the front of a camera lens. It adjusts the intensity of light, giving a video camera operator (or still photographer) more flexibility when shooting.
These filters are used when shooting in bright daylight conditions. For example, if it is midday and you want to capture a nice shallow depth of field the aperture will need to be wide open. Also, if you're looking to get some motion blur as your subjects move around the frame you'll need a lower shutter speed. Aperture and Shutter Speed settings can be hard to compensate for in bright daylight conditions. ND filters allow for all light to be equally adjusted or darkened - they don't block out one color of light more than others, unlike a lot of filters that block only certain colors.
You can typically find ND filters in packages of varying degrees - from about 1 level of f-stop reduction to all the way up to 13 or darker
If I can geek out for a moment: ND filters are measured by the amount of light they remove – this measurement is measured in f-stops. So, a 1-stop ND filter would allow you to get a proper exposure at f/2.8 instead of f/4, or f/5.6 instead of f/8. 2-stop ND filters would let you go from f/5.6 to f/2.8, and so forth.
Test it out: Try to shoot a quick video - put an ND filter on your lens and open the the camera up to the widest aperture setting you can while staying at 1/50th of a second at ISO 100. Now take the filter off and see if you can repeat the process (hint: you can’t without overexposing the video). That will give you a good idea of this concept in practice.
Be sure to check back next Tuesday for the Blank Slate episode about Monopods!